petrochemist

And to do this they require the lens to mounted closer to the sensor than it would be natively (while also adding optical elements). This somewhat reduces the lens/body combinations they can be made for.

That's not infinite (the symbol for which is basically an 8 on it's side) looks more like zero focal length - just as awkward to make :)

M42 lenses come in several varieties. Preset ones - with no auto pin. Switchable Auto - where there is a shut down pin but a switch on the lens disables it Unswitched auto - where the pin must be pressed for the lens to stop down. Canon cameras have no interactions with any of these, but the lens will work fine in fully manual mode if mounted by a suitable adapter. Many adapters have a small flange to depress the pin & allow use of the later unswitched lenses. If I remember correctly all M42 lenses will stop down when used on a flanged adapter - so most adapters now come with the flange. A little work with a file or dremmel tool can remove the flange if it's a major inconvenience, if you can't find any sold without it.

There are quite a few earlier film cameras with built in meters that are not TTL. I suspect the comments relate to these & yes would also be relevant for off camera metering.

There's a very good chance the result will not be neutral. It will probably transmit significant IR, reducing visual light while leaving IR will work but there are much easier ways to get that effect, A variable ND filter set to it;s darkest works if you want to avoid true IR filters. This was taken with a Vari ND filter on a converted camera: PK 28mm vari ND by Mike Kanssen, on Flickr The filters transmission works out close to a 830nm long pass filter (not quite one I've seen available but close enough to a 860nm) Some blue / green filters are poor IR transmitters. I have several X1 filters (green) one of them transmits lots of IR & another is below 50% throughout the cameras IR range & the third is well below 10% throughout the 700-1100nm region. I suspect the difference is down to the anti reflection coatings, but have no ay to check.

If you're after creating a well rounded & meaningful collection then you probably should include iconic examples of all the major camera types as well as a series of landmark firsts. For the firsts perhaps (some are contested): 1888 Kodak No 1 box camera. 1900 Kodak Brownie (bringing photography to the masses) 1925 Leitz (first 35mm stills camera) 1928 Rolleiflex (first practical reflex camera) 1933 Ihagee Exacta (first SLR using 127 roll film) 1936 Ihagee Kine Exacta ! (first 35mm SLR) 1947 Duaflex (first eye level finder) 1948 Hassleblad (first modular medium format) 1948 Contax S (first pentaprism SLR) 1952 Ashai optical's Ashaiflex (first mass produced Japanese camera) 1959 Agfa Optima (first fully automatic camera) 1959 Nikon (first F mount) 1960 Ashai spotmatic (first SLR with TTL & first with spot metering) 1978 Polaroid SX70 Sonar onestep (first AF SLR) 1985 Minolta 7000 (first pro-grade 35mm AF SLR) 1992 Canon first EOS Your range of types should include examples of: Early box cameras, folding cameras, LF press cameras, LF field cameras, LF monorails, TLRs, SLRs, rangefinders, instamatics, 3D cameras, disc cameras, point & shoots, and a few novelties too. Sounds like a big order to me. I've got examples of 8 of these types, but none of the 'firsts' - my brownies are ~30 years later and that's as close as I get!

I guess it might depend on what you call a high-res digital camera. I find generally there's little to no need for such things at all & 24MP is ample resolution (no longer considered high-res). Many of my legacy lenses are perfectly capable of producing excellent images on any of my mirrorless bodies (3 sensor sizes with 12-24MP). Personally I prefer LTM lenses to M42 ones for moderate focal lengths these are very much lighter than the native options. Some of my M42 lenses are heavy & clumsy looking the Takumar 300mm f/4 is the only one that springs to mind. I avoid M42 zooms as the very early zoom designs are generally somewhat questionable quality, with primes this isn't a factor that's noticeable unless you go right back to pre WW2 lenses. Modern native glass is often characterless in comparison to legacy lenses, also in my experience modern lenses are often bulkier & tend to cost quite a bit more, it's not all loss as they tend to be significantly faster :). Most of my adapters are cheaper models than K&F, sometimes they prove a little too short (if short focal lengths are being used) but this can usually be corrected if necessary using some simple shims. Most of my M42 adapters have helicoids built in giving improved close focusing capabilities over more basic adapters. Even with these there little to go wrong!

Did the lens come with the camera? If so I think you must have got a real bargain - I note it's a 50mm f/1.4 not one of the more regular lenses. :)

I've just had a quick play with transmission data I have available for filters - only using transmission values every 100nm. Combining Watten #25 (red), #47 (blue) & #58 (green) I don't see any transmission in the visible, but IR isn't too good either 0.01% @700nm, 0.2% @800nm, 0.5% @ 900nm, & 1% for 1000nm & 1100nm. Changing blue filters the #47 for a Cokin A020, allows transmission at 600nm (total 0.004% through 3 filters) with no more than a doubling of IR The budget 'Photo-R' lighting gels I have might be more suitable if the camera is highly IR sensitive (if not the transmission at 600nm will swamp everything else). transmitting 0.002% @600nm, 0.7% @700nm, 5.5% @800nm, 20% @900nm, 24% @1000nm & 28% @1100nm. To put these into context my budget Chinese IR filters typically transmit over 90% more than 30nm above their cut off & rarely anything more than 30nm below the cut off. Probably also much less issues with reflections & distortions with only a single filter too even if it is only a $20 one. Just playing with tabulated data can introduce big errors. If all three filters transmit at the same visual wavelength that's not in the table, there can be significant leakage, but lunchtimes come to an end so I can't play any longer.

I would say rainbows fit your title perfectly (not being physical objects). Your actual question seems very different though ideas & emotions are near impossible to convey without using the very physical objects you want to avoid.

I seem to remember seeing special papers sold to clean up excess ink from overprinting. Not a problem for me anymore as all mu photo printing is done via an on-line service. The printer at home has been changed to a colour laser, still able to do colour images for the wife & kids yet no more issues with dried up ink.

Use what you have extensively, & only consider a new lens if you find your current two don't let you get the shots you want. Kit zooms are designed to provide the most used focal lengths. An 18-55 would be rather limiting for wild birds where you'd need a much longer lens. Some photographers like using lenses with a much wider view than your lens can manage, even going beyond 180° in some cases. These focal lengths tend to be difficult to compose well with, but there are a number of lenses to investigate if that's where you find you want to go. Macro is another direction your photography might take, it's a challenging field especially if shooting 'true macro' (life size on the sensor). There are many options here particularly as it can be done with accessories rather than a dedicated lens. If your existing zoom covers all the focal lengths you will use you MIGHT decide later on to upgrade it to a more expensive faster version, but there's no need to rush into this. After 10+ years of digital photography I still use kit zooms on all my cameras.

I don't normally have to ask but my wife recently saw my e-bay purchase history for 2020 with the hidden entries showing. Her resulting spending spree may not leave much in the savings.:(

Mine aren't Nikon, but even so yes not just holding on to them but still buying more. I'll even consider adding some screw drive Nikon lenses to my collection if they offer capabilities I don't have already at a price my wife will let me spend.

There is no real wrong or right with IR, so pretty much all of them will be correct even when they contradict 8) Many factors will depend on the camera being used. Many references make a big thing of the focus shift when shooting IR, if you using a mirrorless camera (or live view) this is no longer an issue as your focusing based on what the sensor sees. with DSLRs & film cameras you typically have to focus using visual light then move the focus so the distance focused is by the IR mark (old lenses usually have one - with newer lenses you may have to add your own mark by experimentation). I've always found experimentation is the best way to learn how your camera/lenses/filters work with IR. There are just to many factors involved for on-line information to be totally reliable. I've found a lens that gives hotspots on one of my cameras but not on another, aperture, focusing distance & direction of the sun also can all play a huge roll in hot spots. White balance can also have a big effect but photographers have successfully used: paper, skin, skies, concrete, PTFE... as well as the generally recommended 'fresh grass'. I find various IR groups on Flickr, & an IR forum to be among the most useful sources of inspiration sometimes suggest approaches I wouldn't have thought to try - like using a Foveon sensor with X1 filter to get aerochrom type results; The look of these (SOOC) is very different than my other IR cameras can produce. For comparison I think this was using a 590nm filter (on a full spectrum modified Panasonic GF2) with subsequent due adjustment (easier than the typical red-blue channel swap):

To clarify most IR photography is done using reflected IR using the sun, flash or incandesant lights as the IR source. High subject temperatures are not needed for this. It's actually 'near infra red' that's being used & is very different to thermal cameras. Near infra red will see through many dyes, give high contrast clouds (white against a black sky), show most foliage as bright & see slightly under the skin in portraits typically giving a (much) improved complexion. Wratten #87 (without a letter) is a 760nm long pass and is one of the popular IR gels, Most people prefer a Hoya R72 or equivalent (720nm) Other Wratten IR gels include #87A (880nm), #87B (820nm), #87C (790nm), #88 (710nm), #88A (735nm) & 89B (690nm). I'd suggest the #88 or perhaps 89B would be best of these if using a stock camera as this maximises the amount of IR recorded while effectively blocking all visible light. With a modified camera #25 (Red) is one of my favourites, allowing either false colour shots or monochrome IR. The tip about the TV remote is a very good one - I used it in the early days for checking IR sensitivity of cameras, but not for judging the affects of filters :)

Pentax's mount is actually more backwards compatible than the F mount. Yes there are added features, but all PK lenses work on my Pentax DSLRs, supporting AF if the lens has it. Not only that but the bayonet mount was designed to be compatible with the earlier screw thread M42 lenses just needing a simple in the mount adapter (same mounting flange used) Nikon users make a big thing of their backwards compatibility, then it turns out using pre AI lenses dosen't work - and the wrong combination of lens/body can apparently even damage kit.

If Nikon had $100 for each report over the years that they are going to shut down they'd have enough to keep them in profit without selling cameras! :)

It depends, getting a camera modified is generally expensive (very roughly $250 but varied widely with the company) Some can make a bit of a mess of it too. The first true modified camera I got, I brought preconverted with some cosmetic damage for less than a typical conversion. I've modified a cheap point & shoot myself, but haven't been impressed with the focus. another I tried proved MUCH more awkward to open up. Several older DSLR can work well without modification, The Pentax K100d & Nikon D70 are among the better of these. Some of the Sigma DSLRs have a easily removable dust trapping filter, that also provides the IR blocking function. removing this (30s work on my SD14) makes the camera converted! However it records colour in a different way to most cameras & sees IR almost exclusively in the red channel. Some old Sony cameras have a 'Nightshot' function which makes them IR sensitive my DSC V1 is a point & shoot that only cost £15 and gives IR sensitivity with limitations (forced high ISO, wide open only, green monochrome results)

I've only used them on (full spectrum) modified cameras, As I have ready access to my spectral information while at work I can give a bit of indication - Diskette material transmitted ~0.1% of light at 600nm (red), 0.9% at 700nm (border of red & IR), & 1.6-3% from 750nm to 1100nm (modified cameras IR region) The processed negative gave ~1% throughout the visual, 24% at 800nm, 77% at 900nm & over 80% above 1000nm One of my ND filters gave less than 0.1% in the visual. 20% at 800nm & over 70% from 900nm to 1100nm. these can be somewhat hit & miss as some ND filters block IR too. Stock cameras typically have very little IR sensitivity and will generally see the short IR wavelengths much more than the longer ones. My old K100d which is fairly IR sensitive would probably show IR character with the ND filter and just perhaps (to a lesser degree) with the negative. I doubt the diskette would have been practical.

Not something I've tried, but I doubt it, at least unless you are VERY careful in selecting your coloured filters. I shoot quite a bit of IR & have access to a decent research spectrometer, so have recoded the transmission spectra for quite a few of my filters. IR filters rarely transmit even 0.1% of light at wavelengths more than 50nm below their transition wavelength. Normal coloured filters can - one of my red filters (nominally a 590nm long pass) transmits 4.3% at 400nm (the short end of blue). Most ordinary filters transmit IR, but some of my green & blue ones don't transmit much. I have used a variable ND for recording IR with a modified camera when I didn't have a proper IR filter the right size with me. It's important to remember that while we only see light as three colours it's in fact made up of a continuum of different wavelengths. Having a filter that transmits more light in the 600-700nm region than any other visible band will make that filter look red, but it doesn't mean it reduces the blue & green wavelengths completely or even that significantly. There are plenty of cheap options for trying IR photography, IR filters from China are usually under £20 each (720nm is the basic filter higher numbers are more restrictive & will generally want a converted camera. Shooting through an old floppy disc works (but gives longer exposures which are already long if you don't have a modified camera.) Processed but unexposed B&W film works better, but still not as well as a dark ND filter...

Playing with the scope by Mike Kanssen, on Flickr

Coverage is not really related to focal length. There are limits to how much coverage can be achieved for a given focal length, but most lenses don't approach these limits. My Industar 37 (a 300mm lens designed for large format) covers about 10 times as much as my Samyang 300mm (designed for MFT). All my 10mm lenses (zoom or prime) cover at least three times more than my Pentax 35mm/1.6 (designed for cine)

Available light, shutter speed & DOF requirements, are the main factors, for selecting among the available options. Generally keeping the ISO as low as those requirements allow, till & 600 ISO. Below that it makes very little difference on my main camera unless I want longer shutter speeds. Some of my older cameras tend to stay on ISO200 if at all possible even at minor expense of DOF or shutter speed. I think circumstances have pushed me all the way to 25600 in the past, but as expected noise was bad & there's no real chance of me printing/sharing the results.

There were also a couple of more sophisticated cameras for 110 film. Both Pentax & Minolta made interchangeable lens systems for the format. I use the lenses from my Pentax auto110 on digital, the tiny 24mm/2.8 (only 12.7g) is great fun and nearly covers APSC. The 18mm/2.8 vignettes badly on APSC but covers MFT and at under 30g is also a pretty small lens. Their quality is far more than would have been needed for the 110 film I used briefly back in the day. The body has an excellent viewfinder but the quality of 110 film is not enough to tempt me into shooting film with it today.