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07-12-2007, 04:44 PM   #16
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This has been confusing the heck out of me for a long time, also.
It reminds me of my flyfishing guiding days. It can be very difficult because people have always wanted to flyfish and they will pay $350 or so for a trip and expect to catch fish. But they have never done it and there is a learning curve. So I would take a couple of guys or ladies out for a day and before they had a hope of catching fish they had to learn to cast and how to handle all the line and if we were floating that day the added complexity of casting into moving water from a moving boat. The faster I could get the fundamentals across to a person and get them casting, seeing their fly on the water and ultimately reacting to a strike the better the day usually turned out. But everybody is different. I had to learn to read people and figure out a way to explain to an individual, in a way they understood, how to do all of this. Casting a fly rod is really very easy.......... after a few thousand casts.

So, let me ask the question in yet another way:
I take a picture on a 35mm camera with a 60mm lens mounted on a tripod. Then I take that camera off the tripod and mount my K10D on it with a 40mm lens. I then print both pictures at 4x6. Are they the same??

07-12-2007, 05:20 PM   #17
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QuoteOriginally posted by Col Flanders Quote
So, 90mm (6x7 lens) x 2.875 = 258.75mm

Right?

Thanks to everyone again.
Nope. A 90mm (6x7) lens will give the same view as a [90 x 1.5] = 135mm when mounted on a traditional 35mm camera.

You can do the equation against a 6x7 camera to say that a 90mm lens is the same view as a 258mm lens on a 6x7 camera, but not very many people compare the view to that format.

I had trouble with this at first, too. The only difference between a 90mm lens on a 6x7 camera and a 90mm lens on a 35mm film camera and a 90mm lens on a DSLR is the size of the overall image circle. (The post above shows this well.) You're just throwing away more of the edges when using a large format lens, but you're still cropping to the exact same view. The physical attribute of the lens - namely, that light converges 90mm from the back element - is the exact same.

Put another way, you are not going to get a magical 250mm lens by mounting a 90mm lens designed for a 6x7 camera. You would get the exact same view if that lens were designed for 6x7 film, 35mm film, or digital.


I wonder - did people do this sort of thing back when 35mm film came out, comparing it to medium format film? I suppose they did.
07-12-2007, 05:27 PM   #18
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QuoteOriginally posted by Col Flanders Quote
THAT was NOT my question!

I realize that a 90mm lens designed for a 6x7 camera "appears" the same as a 90mm lens designed for a DSLR.. I am asking about mounting a 90mm lens designed for my Pentax 6x7 mounted on a DSLR with an APS-sized CCD image sensor (such as the K10D.)
That was my answer. I'm saying if you find a 50mm lens made for 6x7 film and a 50mm lens made for 35mm film and a 50mm lens designed for digital - they will all look exactly the same on your camera!

QuoteOriginally posted by Col Flanders Quote
I truely appreciate everyone's help and patience...
We've all been here once!

QuoteOriginally posted by Col Flanders Quote
Let me try asking this way...

If I put a 50mm lens designed for a 35mm camera on a DSLR with an APS-sized CCD image sensor, I no longer have as wide a field of vision. effectively, the 50mm lens has become a 75mm lens.

Correct?
The angle of view is the same as a 75mm lens, yes. But it is exactly the same angle of view as a 50mm lens designed for digital or for 6x7 lenses.

QuoteOriginally posted by Col Flanders Quote
So, what happens when I mount a 6x7 90mm lens on a K10D using the S-mount adapter, of course.
S-mount adapter? Those are for M42 screw mount lenses, which are 35mm film. In order to use a 6x7 lens, you would need to find the Pentax Adapter K for 6x7 Lenses, which I've only ever seen once. The Pentax Adapter K for 645 Lenses I've seen a few times but it is expensive and rare.

Let me ask - do you have some 6x7 lenses, or are you looking to buy them?
07-12-2007, 05:28 PM   #19
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QuoteOriginally posted by Col Flanders Quote
I realize that a 90mm lens designed for a 6x7 camera "appears" the same as a 90mm lens designed for a DSLR.. I am asking about mounting a 90mm lens designed for my Pentax 6x7 mounted on a DSLR with an APS-sized CCD image sensor (such as the K10D.)
Actually I think he did answer your question... "appears" means it gives the same field of view. A 90mm gives the same angle of view as a 90mm. It doesn't matter if one lens is designed for APS-sized CCD, one designed for 35mm, and one designed for medium format... if they are all 90mm lenses, they will all give you the same angle of view when you mount them on the dSLR.

QuoteOriginally posted by Col Flanders Quote
If I put a 50mm lens designed for a 35mm camera on a DSLR with an APS-sized CCD image sensor, I no longer have as wide a field of vision. effectively, the 50mm lens has become a 75mm lens.

Correct?
Well... not really. The lens has not effectively become a 75mm lens. It just gives the same angle of view as a 75mm lens would if you were using that 75mm lens on a 35mm camera. The idea of it "effectively" being a 75mm lens - the "conversion factor" - is only a way of comparing focal lengths on a dSLR with an APS-sized sensor when you are used to focal lengths on 35mm.

So, what happens when I mount a 6x7 90mm lens on a K10D using the S-mount adapter, of course.[/QUOTE]

If the adapter has no glass elements... you will have the same field of view as if you used a 90mm designed for 35mm cameras on the K10d, or as if you used a 90mm designed for the K10d on the K10d. As long as it mounts correctly and there is no optical element in the adapter, a 90mm lens will give the same angle of view as any other 90mm lens, regardless of what format it was designed for.

07-12-2007, 05:30 PM   #20
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QuoteOriginally posted by Eaglerapids Quote
So, let me ask the question in yet another way:
I take a picture on a 35mm camera with a 60mm lens mounted on a tripod. Then I take that camera off the tripod and mount my K10D on it with a 40mm lens. I then print both pictures at 4x6. Are they the same??
Essentially, yes. The angle of view would be the same.

Some people could nitpick that there are slight compression differences (someone talked about the 'feel' of a 50mm lens on film vs. digital) but I think we can discount that for this conversation.
07-13-2007, 04:51 PM   #21
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QuoteOriginally posted by carpents Quote
Let me ask - do you have some 6x7 lenses, or are you looking to buy them?
Yes, I have three lenses for my Pentax 67II.
07-13-2007, 05:44 PM   #22
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QuoteOriginally posted by Col Flanders Quote
THAT was NOT my question!

I realize that a 90mm lens designed for a 6x7 camera "appears" the same as a 90mm lens designed for a DSLR.. I am asking about mounting a 90mm lens designed for my Pentax 6x7 mounted on a DSLR with an APS-sized CCD image sensor (such as the K10D.)

I truely appreciate everyone's help and patience...

Let me try asking this way...

If I put a 50mm lens designed for a 35mm camera on a DSLR with an APS-sized CCD image sensor, I no longer have as wide a field of vision. effectively, the 50mm lens has become a 75mm lens.

Correct?

So, what happens when I mount a 6x7 90mm lens on a K10D using the S-mount adapter, of course.
90mm is 90mm is 90mm. The lens focal length does not change, regardless of what kind of camera it was designed for. A 90mm lens designed for 6x7 will give the exact same magnification and results as a 90mm lens designed for a DSLR, and the exact same results as a 90mm designed for 35mm, with only the following differences:

Due to the fact that the 6x7 lens is designed to cover a very large image circle, it's pretty much guaranteed that there will be no vignetting whatsoever when used on a DSLR. (If there is, it would have been an utterly horrendous lens when used on a 6x7 camera).

Since lenses tend to be sharper at the centers of their image circle than at the edges, the 90mm 6x7 lens will have the advantage of much more consistent sharpness throughout the entire coverage of an APS-C sensor.

In short, you will see absolutely no differences in terms of field of view between lenses of focal length X, regardless of what kind of camera they were designed for. You may see differences in terms of vignetting and quality since you're shooting through a lens that was designed to provide good quality over a much larger image circle.

Of course, for the same reason, a 90mm 6x7 lens is going to be MUCH larger and heavier than a 90mm lens designed specifically for a DSLR.

Also note that while APS-C DSLRs require far less image circle coverage, because the sensor of all DSLRs is much more reflective than film, DSLRs have more stringent requirements than film cameras in terms of internal reflections within the lens.

For many higher-end lenses (such as Pentax SMC lenses), this doesn't matter much since Pentax SMC is about as good as you'll get in terms of reducing reflections from optical elements, and I believe most of the SMC Pentax lenses also take care to ensure that no other element of the lens is too reflective. Lenses from other manufacturers may not perform as well though. This is why you now see lenses that provide full frame image circles that are marked as "Optimized for Digital" or "Digital Integrated" - extra care has been taken with such lenses to reduce internal reflections.

Examples of such full-frame-with-digital-taken-into account are the Sigma DG series and the Tamron Di (not Di II) series.

An example of a lens that provides acceptable results on film but horrendous contrast on a DSLR due to too many internal reflections is the first generation Sigma 28-200 3.8-5.6. It served me well on my old PZ-70 but was unusable on my K10D.

Chances are that most if not all 6x7 lenses will have good multicoatings though.
07-26-2007, 04:05 AM   #23
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Col Flanders is asking a very simple question to which reams of theory and calculations have been given in reply. Looking at his responses, I cannot help but recall the verse of Khayyam (as translated from Pharsi by Fitzgerald):

"Myself when young did often frequent
Doctor and Saint and heard great argument
But ever more,
Came out of the same door as in I went!"

So let me add to the haze as well! (I shall discuss this in round figures, not decimals, etc.!)

Col Flanders, this is the way I see it: A 67 format 90mm lens will be equivalent to a 45mm lens on a 35mm film SLR. A 45mm lens on a standard non full frame digital SLR like the K10D should be equivalent to a 67mm lens. Trust this is what you are looking for.

To confirm this is so, just mount any 35mm format lens covering 70mm on your digital SLR, zoom to 70mm and check the coverage. Then replace it with the 90mm 67 lens+adapter and check the coverage; it should be more or less at par.

07-26-2007, 04:54 AM   #24
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Nope, you missed the point..... If you stick a "full-frame" 70mm lens on your K10D, it will give you a certain field of view (approximately the same FOV as if you stuck a 105mm lens on your 35mm film camera). If you stick a "APC-C" 70mm lens on your K10D, it will give you the SAME field of view as the other 70mm lens.

If you stick a 90mm 67 lens+adapter, you will NOT get the same coverage as either 70mm lens, because 90>70

The "adapter" just changes the mount, it doesn't change the focal length of the lens.

All your Fitzgerald poetry doesn't change the fact that a 70mm will ALWAYS be a 70mm lens, and a 90mm lens is ALWAYS longer than a 70mm lens....(when mounted on the same camera)

QuoteOriginally posted by Khukri Quote
To confirm this is so, just mount any 35mm format lens covering 70mm on your digital SLR, zoom to 70mm and check the coverage. Then replace it with the 90mm 67 lens+adapter and check the coverage; it should be more or less at par.
07-29-2007, 02:26 PM   #25
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This thread confuses the hell out of me.
07-29-2007, 02:44 PM   #26
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My head hurts SO.

A 90mm SLR and a 90mm 6x7 will behave the same on DSLR (1.5x crop factor)

Is that it?
07-29-2007, 06:18 PM   #27
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QuoteOriginally posted by countzero Quote
My head hurts SO.

A 90mm SLR and a 90mm 6x7 will behave the same on DSLR (1.5x crop factor)

Is that it?
yeah, what's the final crop factor for a 6x7 lens?
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