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Why no posts?

I'm amazed to find absolutely no posts in the lenses section, surely most photographers use them for every shot & they make a huge difference to the results!
A large part of my photography is exploring what I can do with adapted lenses - the answer MAY be nothing much, but that's usually down to my artistic skills falling behind my Geekery.

I have made a few images without the aid of lenses (pinhole photography, photograms) but they've been a very small part of my photography, and I've probably done much more than most :geek:
 

Asher Kelman

OPF Owner/Editor-in-Chief
Feel free to add to the lenses section. Way back this was critical as we were trying to adapt to a limited supply of inexpensive solutions.

But then some lenses have such special value, like tilt-shift or soft focus lenses, that it really enriched us.

So please go ahead and share with us on lenses and Ford sure you will make me happy!

Asher
 

Jerome Marot

Well-known member
The posts about lenses are in the section "Pro class cameras with interchangeable lenses" and were not moved here when this section was opened.
 
The posts about lenses are in the section "Pro class cameras with interchangeable lenses" and were not moved here when this section was opened.
I suspect most photographers wouldn't class my cameras as 'pro class' though it seems security at events generally do.
I use several cameras with interchangeable lenses - MFT, PK, Sony-E & Sigma SA but only the A7ii has actually been classed as high as semi-professional in any of the reviews I've seen.:rolleyes:
 
What exactly do you want to know about lenses? Maybe we can help.
The list is far too long to write. It might be easier to list what I don't want to know :)
Mind you for that to be any use I'd have to disclose what I think I know about lenses too (which would again take me ages)

I frequent quite a number of photo forums, and over the years have stumbled across many interesting tips, in reply to other peoples queries. Dr Klaus Schmitt's blog has also proved very useful to me, suggesting a few lenses that transmit UV without being excessively expensive. Then there have been various things I've seen on adapting, modifying or home building lenses . Loads there I've yet to try - flipping elements on some of my surplus 50mm primes may be the next experiment
 

Jerome Marot

Well-known member
The list is far too long to write. It might be easier to list what I don't want to know :)
Pick one first question, maybe we can go somewhere from that.

Mind you for that to be any use I'd have to disclose what I think I know about lenses too (which would again take me ages)
Same as above: pick one think you know about lenses.

I frequent quite a number of photo forums, and over the years have stumbled across many interesting tips, in reply to other peoples queries. Dr Klaus Schmitt's blog has also proved very useful to me, suggesting a few lenses that transmit UV without being excessively expensive. Then there have been various things I've seen on adapting, modifying or home building lenses . Loads there I've yet to try - flipping elements on some of my surplus 50mm primes may be the next experiment
You realize that optics can be computed, e.g. by ray tracing programs, don't you?
 
Ray tracing programs only really work well when you know a lot of info about the types of glass involved and there specific curvatures.
The refractive index of glass varies with wavelength - I play with NIR increasing the range of wavelengths beyond most lenses design so chromatic aberration could be more of an issue than for purely visual uses. Standard historical achromats use competing lenses of crown & flint glasses to make a combination where all wavelengths of visual light focus much closer to the same point than we'd get with a single simple element.

Picking available elements at random I wouldn't even recognize which were crown glass & which were flint glass. In lenses there's actually a much wider range of glass types used . With the aid of kit at work I could possible identify a few of them Calcium fluoride (from it's mid IR transmission) & pure quartz (UV transmission) the bulk of the others I can spot are technical glasses of more use in filters than lenses. I don't have the means to determine the curvature of the surfaces to any useful level of accuracy either.

Combining achromatic doublet of known focal lengths to get basic telephoto or retrofocus designs is something I don't need ray tracing for. Simple application of formula available on-line (IIRC they're on the homemade lenses group on Flickr and added into a spread sheet I have) will calculate combined focal length & back focal length, from the individual doublets focal lengths & their relative spacing. Of course the aberrations from such simple designs will be significant, but that's half the fun of experimenting. The only trouble is finding the time to build it - I may still be years away from building my own experimental lenses from scratch. :(

Quick modifications to existing lenses are much easier. I have two in use where the rear group has been removed;
The 50mm I did this to became a soft focus lens of about 100mm focal length (I stick it on bellows to focus, the soft glow decreases rapidly as the aperture is closed down). Here's an example fully open
soft focus mod fully open by Mike Kanssen, on Flickr

Another lens (a soligor 105) had a badly fogged rear group that proved more difficult to clean up than I'd hoped. Trying it without the fogged elements left me with a lens of roughly 200mm focal length & much higher contrast (again needing extension to focus). I was surprised that aberrations in the remaining lens are not particularly noticeable.
an example of that :
Soligor 105 without rear group by Mike Kanssen, on Flickr
From what I hear flipping elements on some normal lenses (the Helios 44 is the usual subject) also creates a soft focus effect but with 'crazy bokeh' too. The mod, is simple & reversible & I have several spare 50mm lenses so I'll probably get round to trying it with both front & rear elements (both reportedly work but give different effects) sometime before I retire.
 

Asher Kelman

OPF Owner/Editor-in-Chief
Well, for me, there’s no consideration of building lenses from scratch even with formulas online.

I find that available Pentax and Leica Mount Lenses and Canon FD primes are bargains and so many adapters are present.

Miraculously, there is now an AF adapter for Leica lenses on Sony Alpha series bodies!

Pretty amazing.

I have adapters for my MF Fuji 50 MP GFX to use AF with Canon lenses and also MF with Bronica Sq and Pentax lenses!

I would like an AF adapter for Hasselblad AF lenses as they have Leaf Shutters allowing leaf shutter flash at 1/500 second, perfect for overpowering the sun!

Asher
 
Well, for me, there’s no consideration of building lenses from scratch even with formulas online.

I find that available Pentax and Leica Mount Lenses and Canon FD primes are bargains and so many adapters are present.

Miraculously, there is now an AF adapter for Leica lenses on Sony Alpha series bodies!

Pretty amazing.

I have adapters for my MF Fuji 50 MP GFX to use AF with Canon lenses and also MF with Bronica Sq and Pentax lenses!

I would like an AF adapter for Hasselblad AF lenses as they have Leaf Shutters allowing leaf shutter flash at 1/500 second, perfect for overpowering the sun!

Asher
Yes the Techart Pro is a lovely little toy and easily adapted to the PK, M42, OM, LTM lenses in my collection too. I do wish it was a bit more robust though, it's pushing the limits to use it on a 500mm lens (ONE of my mirror lenses is just light enough). It doesn't work on my NEX6 either

I've not played with Fuji cameras or lenses, but have tried quite a variety of SLR, rangefinder etc mounts on several mirrorless systems (now in 3 different crop factors). Sadly medium format is something I could only hope to play with via film, and the hardware I've collected for that is hardly impressive - only fixed lens antiques.

There are bridge cameras around with leaf shutters, which would prove much cheaper than going via Hasselblad lenses, but I don't suppose for a second the results would live up to your GFX!
 

Asher Kelman

OPF Owner/Editor-in-Chief
..... There are bridge cameras around with leaf shutters, which would prove much cheaper than going via Hasselblad lenses, but I don't suppose for a second the results would live up to your GFX!
But one can use a leaf shutter Hasselblad lens in Manual mode!

If one focused carefully and then used f16, the depth of focus would cover a lot of errors and one could just not refocus for that part of the shoot!

Asher
 

Asher Kelman

OPF Owner/Editor-in-Chief
Another way around not having a leaf shutter, is to start the shoot when the sun is low or to use a giant translucent scrim overhead to tame the sun, no matter what!

Asher
 

Jerome Marot

Well-known member
Hasselblad H lenses (the ones with AF) have a central shutter which works up to 1/800s, not 1/500s. They are not very expensive used and an adapter to the GFX is sold by Fuji, which shares rights with Hasselblad to the H bayonet. AF is not supported, but would be too slow to be usable on this kind of lens anyway.
 

Jerome Marot

Well-known member
Ray tracing programs only really work well when you know a lot of info about the types of glass involved and there specific curvatures.
I meant that the people who design lenses have access to that info and to raytracing. They chose each element in a lens for a reason. By picking and matching elements at random, you are not likely to find anything as good.

The refractive index of glass varies with wavelength - I play with NIR increasing the range of wavelengths beyond most lenses design so chromatic aberration could be more of an issue than for purely visual uses. Standard historical achromats use competing lenses of crown & flint glasses to make a combination where all wavelengths of visual light focus much closer to the same point than we'd get with a single simple element.

Picking available elements at random I wouldn't even recognize which were crown glass & which were flint glass. In lenses there's actually a much wider range of glass types used . With the aid of kit at work I could possible identify a few of them Calcium fluoride (from it's mid IR transmission) & pure quartz (UV transmission) the bulk of the others I can spot are technical glasses of more use in filters than lenses. I don't have the means to determine the curvature of the surfaces to any useful level of accuracy either.
If the surfaces are spherical, the curvature can be determined by comparing the power of the lens when put into mediums with different refractive indexes, for example air and water. Then, the lens is measured at different wavelengths to determine the characteristics of the glass.
 
I'm not expecting to make 'anything as good', modern lenses are often far too good, completely lacking character. Anything I make myself is unlikely to be anywhere near as good as lenses from 100 years ago, where skilled designers did complicated math to come up with designs like the Tessar, Biotar, Gauss which show character but are fairly well corrected.

The idea of using liquid of different refractive indexes is an interesting one I have access to many more of these than most people, as well as kit for measuring the actual refractive index of liquids. Sugar solutions are great for creating liquids of different refractive index, being able to produce any RI between 1.333 & ~1.48, but without being able to accurately measure what you've made they're not very helpful. We have a wide range of solvents in the lab covering a RI range of 1.328 to 1.628 but I'm not using methanol or CS2 for this sort of thing!

The data I have on refractive indexes only gives a single number or a range for each material. I would expect the actual refractive index for all materials to vary with wavelength (as well as temperature), so the values are probably average for visible light or perhaps using the sodium D lines. I couldn't convert the labs automatic refractometer to use different wavelengths, but it should be practical with the old Abbe refractometer.

If the lens has the same curvature on both sides it would be practical, but I'm not sure building a vertical optical bench (so I can just immerse one face) is something I have the space for. I'll have to give it some thought, thanks for the idea. :)
 
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Asher Kelman

OPF Owner/Editor-in-Chief
I agree that many modern lenses are too accurate even to the edges to have “character”. But we can do a lot in photoshop of creating imperfection that’s adorable!

Vignetting? Yes!

Drop off of clarity? Perfect!

A giant scratch on the front element, hand me that fine black magic marker to ink it in!

Asher
 
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