What is critical to sharpness - back or vacuum insert?

[milan_moudgill]

Here is what may be a very basic question...

 

Having read more than a few posts on supposed lack of sharpness - resulting

in brand new backs being sent back for repair/service, got me convinced that i

should not compromise on the back/insert and not risk getting a second-hand

piece.

 

So I paid extra dollar, ignored eBay, and got a brand new 220 vacuum insert.

 

But my back is a second hand piece.

 

Which got me thinking... what is critical to sharpness... the back or the insert?

Or the combination is the key?

 

Can anyone shed light here? Have I been stupid and got a new insert in

reaction to the reported problem, where I should have looked at a new back

as the critical component contributing to sharpness?

 

Thanks

 

Milan

[ellis_vener_photography]

What is most critical is making sure the groundglass screen and the film plane are actually

in alignment. If your camera has autofocus --You have an AF Contax right?-- you have to

make sure that is working properly. After that comes testign the lenses to find out where

the "sweet spot" is for optimum lens performance, and afterthat will come film alignment

issues.

 

Before spending that money I would have actually tested my system to see if other

people's reported problems are real problems for my system.

[lee hamiel]

Milan:

 

I am pretty certain it's the insert that contributes to the sharpness aspect - provided that the back seats properly.

 

I do not think you made a mistake buying a new insert.

 

I will email you a sectional drawing offline.

[q.g._de_bakker]

Critical sharpness of the image of an object depends on how the film follows the curvature of the "plane" of sharpness in the image the lens produces, and on how flat, or curved, the object to be imaged is.<br>Sometimes, having a completley flat film is not the way to get the most sharpness. ;-)<br><br>What would concern me most however is the availability of 220 film. There always have been few emulsions to choose from, and the number is rapidly decreasing. As is the number of shops stocking 220 film.

[colin_elliott]

Milan, I purchased the vacuum back some years ago for my Contax 645.

To the naked eye, there seems no visible difference compared to the regular insert.

As a 220 film user I just thought it would be a reduction of possible weak links.

 

There is less emulsion choice in 220 films, however, I have few favourites when it comes to film and they are all readily found in 220 . e.g. Velvia 50 (and now the new 100); NPS 160; NPC 160 and Reala. Provia 100 is also available but not one I use normally. There are a few Kodak offerrings as well. Depending on your usual film stock, you may find other choices.

[milan_moudgill]

Ellis! Always the wise overview - Thanks!

 

Sorry... I forgot to mention this was a Contax 645 question.

 

The film availability issue... I am using Velvia 50 more and more. For now it

seems my immediate needs are covered. In the future, whether 220 will

become even more scarce is a question that is as pertinent as - will digital

completely kill film. Something that I am happy to live with.

 

... and how does one figure the 'sweet spot'? Is this data available? Is it

different from lens to lens, even if both are the same focal length?

 

I have a 45, an 80 and am looking for a 120 and a 210

 

Thanks

 

Milan

[ulrich_ploedereder]

Hello Milan,

 

I've shot several pictures which where definitely out of focus (partially in the upper third of the image) because of film bending so I bought a second magazine with the vacuum insert. Therefore I switched to 220 film. But I can't see any visible (!) difference between a 220 film in the standard magazine and a 220 in the vacuum magazine.

 

Regards

 

Uli