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08-23-2010, 08:10 AM   #1
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Stupid question, or brilliant idea?

Stupid question, or brilliant idea?

OK, so this might be a stupid questions, or possibly a brilliant insightful idea. I donít know, so I thought Iíd bring it to everyoneís attention. For that matter many of you might simply wonder, ďwell why the hell would you want to do that anyway?Ē

So Iíve been thinking about the whole issue with crop factor on APS-C sensors and how they affect my film lenses. Basically, all my old film lenses now act like they have much longer focal lengths then they did on a 35mm film camera. In some situations thatís not a bad property. I can use a common 200mm zoom lens as a 300mm lens that I would have paid much more for. Great right? Well not always, you see, Iíd like the wide end of my zooms and for that matter my wide primes to be wide again. I especially donít like the idea that my Pentax-a 28mm f2.8 acts like itís a 42mm lens.

So the question is, does anyone make, or plan to make a reverse teleconverter of sorts that would shrink the output image size of a film lens down to that of an APS-C sensor? Just wondering because I have some lenses that would be great as a single lense solution for walking around if only they acted like they did on film cameras.

08-23-2010, 09:00 AM   #2
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The focal length of your lenses doesn't change, regardless of what you mount them on. Here's an article on that: https://www.pentaxforums.com/forums/pentax-lens-articles/90477-crop-factor-fo...ield-view.html

So, basically, a larger image is being covered than the sensor can see. If you wanted to convert the whole image so that it fits perfectly on an APS-C sensor, you'd have to have some really complex optics which are likely not feasible, and would probably screw up the image quality more than they are worth

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08-23-2010, 09:17 AM   #3
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I typically don't like using any glass that changes the properties of the lens in any way. I suppose it could be done, you can buy a wide angle attachment for the lens front, but I prefer to simply go to a wider lens. I also prefer to forget about the crop factor. I really means nothing in the grand scheme of things and if the 28mm won't do it, get a 15 or 16 mm lens.

08-23-2010, 09:32 AM   #4
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It's been a while since I designed a lens, but I believe a field of view increasing adapter would need to mount in front of the lens, as present adapters do. A tele-converter works by spreading the image of the main lens. A converter mounted next to the body could not add image area that the main lens does not capture.

08-23-2010, 09:40 AM   #5
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I've only seen wide angle adapters that screw in at the front of the lens, not the back. They also give you a nasty fisheye perspective.

The 1.5x multiplier term is misleading. It doesn't actually multiply the focal length since the distance to the sensor plane remains the same. It simply crops it to give a similar effect at the cost of losing mega pixels. If you cropped an image enough, you can turn a 50mm view into a 500mm view, you'll of course, notice some serious image quality degradation.
08-23-2010, 12:22 PM   #6
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Adam gets what I'm trying to say. I'm looking for a way to convert the image coming out of a standard 35mm film lens to fit onto the APS-C sensor so that there is no crop factor. Basically something that narrows the light coming out of the back of the lens. But alas, according to Adam it is probably not feasible and definitely does not exist.

I have a wide angle converter made by Olympus, it actually works very well, but it only has a .8 multipier so it doesn't totally counteract the crop factor of an APS-C sensor for which I would need one that had a multiplier of .667. The wide angle converter I have does not add a 'fish eye' look, nor does it distort the image. It does lower the available light level a bit, making indoor shots (for which I purchased it) a little harder, but otherwise it is essentially transparent to the camera. I don't like using it except for indoors because it's so HUGE that it is very susceptible to flare outdoors. Otherwise i'd probably use it on some of my lenses to attempt the correct the crop factor somewhat.

Anyway, thank you all for your help, if anyone knows someone at Tamron, Sigma, Tokina, or Pentax, you may want to suggest this idea to them and see if it's possible.
08-23-2010, 12:41 PM   #7
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I think we all get what you are saying and are suggesting that it wouldn't really be desirable, if even possible.

08-23-2010, 01:06 PM   #8
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Damian, do you have some kind of a problem with LBA?


08-23-2010, 01:10 PM   #9
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Another thing:

With today's high resolution DSLRs, there's no reason to work backwards with long focal lengths trying to convert them to wide. You're better off shooting wide, and cropping to replicate the longer focal length when needed.

High resolution sensors, quality lenses, and computer post-processing has negated many of the concrete requirements of using a particular focal length in a given situation.
08-23-2010, 01:56 PM   #10
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QuoteOriginally posted by Ira Quote
High resolution sensors, quality lenses, and computer post-processing has negated many of the concrete requirements of using a particular focal length in a given situation.
You forgot the "pixie dust" factor, Ira. But since you feel that way, I'll be happy to take your ST35/2, ST50/1.4, and ST105/2.8 off your hands for a nominal fee. Mmmm, better throw in the ST85/1.9 also. Always glad to help.

@OP,
How to make a lens on an APS-C camera act wider:

* Screw a sucky wide adapter in front of the lens. Ewww...
* I read that backing up 10 ft / 3.3m is like going 1.5x wider.
* Use wider glass. Anamorphic cine lenses are great!!!
* Shoot into a convex mirror. Objects may be closer than they appear.
* Get a 645 or 6x6 cam. Insert a 135 cart. Sprocket-hole panos!
* Shoot an ordinary shot. Tastefully make it wide-angle in PP.
* Rewrite the laws of physics / optics. Anyone can now.
08-23-2010, 01:58 PM   #11
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Ira, yes I'm struggling with a little LBA problem. Hopefully it won't consume me (and my bank account) entirely.

This whole Question here started in my mind last night as I lay awake in bed. I kept thinking, "If they can make a 18-250mm lens, why can't someone figure out how to just make a film lens to APS-C adapter that will get rid of the crop factor". It just seems odd to me that there are such things as 2x Teleconverters (which I own a few) that do what they do, but there is nothing that goes the other way. I understand the drawbacks of additional elements. When I use my Teleconverters (doing macro) I run into a lot of PF on highlight edges. Thankfully it is easily corrected on the computer. Regardless, it seems from everyone here, that there aren't going to be any 'Crop Correctors' anytime soon, so I guess I should just forget it.

I get what you're saying though about shooting wide and then cropping down, but i'm just a bit of a stickler for taking a good picture the first time without having to do a bunch of cropping to get the frame just the way I want it. I guess I'm just going to have to invest in a Tamron 18-200mm Di.
08-23-2010, 02:14 PM   #12
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Thanks for the "advice" there RioRico. I'll be sure to "back up" and not use my "sucky" wide adapter on any of my sharp primes. I'd love to use wider glass if I could afford it. The whole point was to not have to buy wider glass, when I have wide glass. My DA L 18-55 is plenty wide, and so WAS my Pentax-A 28 f2.8 until now. The issue is I have a Pentax 35-105 and I'd love it if the 35mm end actually acted like 35mm. It's an issue with occasionally not being able to "back up" far enough to get a wide enough shot. Believe me, I like my 18-55, it's wide enough, but sometimes it's just not long enough. There are other old gems out there that would serve me well as a one lens solution, but unfortunately, the wide end will never be wide enough with the 1.5x crop factor.
08-23-2010, 02:18 PM   #13
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QuoteOriginally posted by Damian Quote
I get what you're saying though about shooting wide and then cropping down, but i'm just a bit of a stickler for taking a good picture the first time without having to do a bunch of cropping to get the frame just the way I want it.
That is an admirable goal, Grasshopper. It is not necessarily a realistic goal. Reality has a nasty habit of placing us in locations we might not prefer. We use zooms and other tricks to try to circumvent reality, but reality usually wins anyway. Bother. My DA18-250 just isn't quite enough...

I started shooting before zooms existed. My first zoom was on a camcorder in the 1990's -- or rather, before then I zoomed with my feet. With film, I made my own prints. Darkroom work always involved cropping, rotating frames to straighten images, burning and dodging, creative application of nose grease, etc. PP is part of the process of making a picture. [NOTE: Taking a picture is not the same as making a picture.]

No matter the sophistication of our tools, we hominids are imperfect creatures. We need all the assistance we can get. My late bro-in-law, a painter and police chief, quoted Picasso "There is no cheating in art." Do whatever it takes to produce the image you want -- that's the only rule (except in arbitrary contests).
08-23-2010, 02:56 PM   #14
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Very true, I completely agree, but non the less, my previous statement still stands. Everything has to be cropped, at least a little, the fun part is trying to take pictures where there is more of the original image left then not. Don't let my age fool you, I too started in film and dark rooms, cropping, dodging and burning, using filters on the enlarger to increase contrast and mastering the art of over or under developing to achieve the perfect contrast and tone. I burned through an entire pack of photo paper one afternoon, trying to get the perfect prints.

I've been using PhotoCHop since before most knew it existed, and I think it's a wonderful tool. I've done some amazing things with total Crap using Photoshop. There is absolutely nothing wrong with using whatever tools are at hand to achieve the result desired and the occasional oops that produces a result that you didn't know you desired. I simply prefer, in most cases, to limit how much PP i have to do to achieve the results I'm after. Call it a personal idiosyncrasy, but to me (and I know you don't agree) cropping out more then half the image is kind of like cheating. It's just one of those things.

For the record, there are purists out there that would argue the point of taking a picture vs making a picture. Personally, I was always better in my early film days, when I had one prime 50mm lens, at 'making' a picture then taking one. But to be fair, although my darkroom skills far exceeded many of my piers, most of the time, those that took the best pictures ended up with the best results on paper. I know that film grain isn't an issue any more, but back then it was, so I taught myself how to 'take' a good picture in order to improve my results. That attitude kind of stuck with me I guess.
08-23-2010, 05:33 PM   #15
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QuoteOriginally posted by Damian Quote
For the record, there are purists out there that would argue the point of taking a picture vs making a picture. Personally, I was always better in my early film days, when I had one prime 50mm lens, at 'making' a picture then taking one.
There's no arguing your point here at all--you're right.

It's just that things change, and in those days, you HAD to take the picture, unless you processed and printed yourself--where you were in effect making the picture anyway.

I'm no great artist. I'm just looking to capture some memorable images that may touch someone, and whatever the hell I have to do to make that happen, I'll do.

I ain't no Ansel Adams, and I know it.
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