Focusing problems with MF slide projector

[sorry_no_photos]

<p>I find that my 645 slides on a 1960's vintage Rollei slide projector can't be fully focused all at once. Usually there is a choice between focusing the centre of the shot or the periphery. Just wondering if this is due to the poorer optics of a 50 year old lens or whether there is something inherent to slide projection that causes this. The same slides can be put in my Epson V700 scanner and there are no problems with focus. <br>

The slides haven't bowed due to heat (I've put a cooler halogen bulb in the unit and the temp inside the unit is only about 30 degrees celsius after about 20 minutes). <br>

Thanks in advance.</p>

[Robin Smith]

<p>It inherent to all slide projectors - arguably worse with MF. Glass mounting the slide is the only way to solve it - although that introduces other concerns such as dust, anti-moire shadows, fungus, condensation. Some projectors are better than others - sometimes warming the slides first helps a little.</p>

[clay2]

<p>The slides are bowing in the projector gate. Only solution besides mounting in glass is<br>

a curved-field projection lens. Evil-bay may have something for you.<br>

Best regards,<br>

/Clay</p>

[sorry_no_photos]

<p>Thanks for those answers. I just did a scan with one of the slides that was problematic. Everything was in perfect focus from edge to edge, and I couldn't detect any bowing of the slide (other than the usual minor displacement that usually occurs without glass...I'm guessing on the order of about 0.1 mm). So if bowing occurs, it must be on a very short term basis in the projector. Is bowing due to the ambient heat? Or is there some other light frequency that causes it? <br>

A related question: if I use glass mounts, will I then run into problems with scanning? </p>

[Giovanni Cappai]

<p>Evan, I have a P.11 Rollei projector. There is an array of lenses between film and lens and especially one of them is of extreme design with a very long shape. Is it possible one of these lenses is missing in yours? I'm not sure if you are talking for the same projector...</p>

[david_smith35]

<p>Evan, I use a medium format projector, and glass mounting is essential if you want a fairly uniformly sharp image. I say fairly, as GEPE mounts (about the best of a bad bunch) still leave a small air gap between the film and glass, which occasionally results in a slightly less than perfectly sharp screen image.<br />There's no problem scanning a glass mounted slide, and in fact it's better than using the crappy film holders supplied with the scanner. I scan with slides face down so that I'm scanning through the non anti newton part of the mount.<br>

By the way, what do you mean by a cooler halogen lamp? Lower wattage?</p>

[sorry_no_photos]

<p>Thanks David. I did order some Gepe glass mounts yesterday, so I'll see how that works out. Good to know that they'll still permit scanning. The halogen lamp is the same wattage, but supposedly they're signficantly cooler than conventional Sylvania incandescents (and it seems the 30 degrees mentioned above supports that, though I didn't do the same test before I made the change). Do the glass mounts just have one layer of glass? If so, is the glass supposed to be on the lens side of the slide or on the bulb side?<br>

Thanks Giovanni. Yes, I have the P11, and yes, there are the two removable lenses between slide and bulb, and the removable parabolic unit behind the bulb. Just wondering if a Hasselblad projector would be appreciably better in terms of optics.</p>

[david_smith35]

<p>Evan, The mounts have a piece of glass in each half of the mount - the white part of the mount contains the AN surface glass, and this should face the shiny side of the film. Mount your slide emulsion side down in the grey half of the mount. When projecting, the white side of the mount should face towards the light source.<br>

The mounts have to be cleaned before use (a right PITA!) and require the patience of Job to remove all the dust. Best of luck! BTW, don't leave them in the projector gate for too long - the 'greenhouse effect' means the temperature inside the mounts will be way higher than the outside air temperature, and it's easily possible to overheat the film.<br>

I've used a Hasselblad projector, and it's a nice peice of kit but optically no better than my regular Leitz projector. It also projects a slightly dimmer screen image (in spite of being the same wattage) due to the design of the internal mirror system.</p>

[sorry_no_photos]

<p>Just finished mounting and projecting and scanning some slides in the Gepe glass slides. Although they're still not perfectly flat for the projecter, I'm quite satisfied. I noticed a couple of slides with newton rings initially, but when projected they seem to have disappeared...and now I can no longer find them in the light box anyways. No problems scanning. No issues with the greenhouse effect...possible due to the lower temps of the halogen bulb. (I'll have to select a poorer slide and time it under projection to see exactly how long it takes to ruin the slide). <br>

I don't get obsessive about removing all the dust before mounting, but still get good results with a Giotto blower bulb (very good design for this purpose) to get rid of 90% of the dust on the mounts and slide before mounting. With a bit of practice, I found I could mount a slide in a couple of minutes. If I've got a problematic dust mote, I can often just rotate the mount so that the mote is not in a sky portion of the slide image. <br>

I may try a camel hair brush next time, though. I've heard that if you blow air on the brush, it causes it to have a small electrostatic charge, which can attract dust off of a slide. So I'll try that next time I get some more mounts from Gepe.</p>

[sorry_no_photos]

<p>There's something magic about these slides. The heft. The Lilliputian size. The smooth finish of the plastic. The colors and detail when held between a light box and a magnifying glass (and my reading glasses). I don't think even a good print from my Canon 5D can match the visceral experience. Nor can the projection of the slide itself, which loses quite a bit of the detail on the slide and still has some of the focusing problems mentioned above. Nor can a scan, which also loses detail.</p>

[david_smith35]

<p>Evan, I'm surprised you have newton rings - I take it you're using AN mounts? It's a good idea to do what you suggest and use a scrap slide to find out how long it takes to overheat in the slide gate of the projector.</p>

<p>I wouldn't describe MF slides as lilliputian - this applies more to 35mm! I envy your ability to mount a slide in a couple of minutes - it takes me considerably longer. I am however, very fussy about removing practically 100% of the visible dust from the mount. I also agree with your comments about the visual impact of a slide compared to a print.</p>