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02-16-2009, 02:07 PM   #76
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QuoteOriginally posted by ray94553 Quote
For all those worried about my interpretation of crop factor. I've been corrected on this many times. But I think my way of saying is just fine
No, unfortunately it is not fine, it is plain wrong.

QuoteOriginally posted by ray94553 Quote
It just seems obvious to me that the focal length remains the same but the field of view covered is varied by the "Crop Factor". Notice that I said; "LIKE" having an 870mm 4.0 lens. This is because the field of view is cropped to a view presented is similar to that of an 870mm lens at that same lens to subject distance, while angle of view and the aperture (DOF) remains the same.
You were talking about a 300mm lens. So, there is no way, that this would be equivalent to a 870mm lens. No, it does not behave as such.

A 300mm lens on a APS-C crop sensor "behaves" (gives you the angle of view) of a 450mm lens on 35mm film or full-format. And the same angle of view as the 870mm on 6x7! It is exactly the other way round.

QuoteOriginally posted by ray94553 Quote
Also another possible advantage gained is that you’re using the center of the lens and therefore you may see less edge distortion depending on the lens.. I stated things this way so as not to confuse anyone into thinking that the image is actually cropped.
We had that discussion futher above. I think, the conclusion is, that generally lenses made for larger formats are designed with less resolution, than lenses of the same focal length for smaller formats. But this does not rule out, that certain MF/LF lenses are so excellent as to be very useable on smaller formats, too. Then your observation is competely true and the advantage may be, that the lens for the larger format delivers the same quality as a lens made for the smaller format.

QuoteOriginally posted by ray94553 Quote
If I take a 10 megapixel image and crop it by a factor of 0.5, I have lost half the data and half the pixels. The image is smaller it is no longer a 10 megapixel image and it can only be printed at half the size of the original. On the other hand an image, created by a lens and camera body combination that has a crop factor of 2, that 10 megapixel image will have half the area of view of a lens of the same focal length with a crop factor of 1. However, in order to “zoom in” without loosing data and pixels, and staying with a 35mm lens on a 35mm camera body, you would need a lens with the longer focal length.
Sorry, I don't quite understand, what you mean. I can follow the first three sentences, but don't get, what you mean with the "zoom in" statement.

QuoteOriginally posted by ray94553 Quote
While a 6x7 300mm lens mounted on a 2/3 sensor digital camera body may not produce an exact 870mm focal length image, for the money it’s a darn close cousin.
If anyone can find a better shorthand way of describing this relatively simple rule of optics please tell me.
No, this is completly wrong! A 870mm lens used on a 6x7 camera would provide you with the same angle of view on that camera (if we forget side ratios for the moment) as a 300mm lens gives you on APS-C. AND ANY 300mm lens will give you exactly the same angle of view on your APS-C camera, whether its made for 6x7, 6x6, 35mm or APS-C or even 5x4 inch.

QuoteOriginally posted by ray94553 Quote
As for the tilt lens, while I have never used a tilt only lens on a camera I have used the tilt shift on a 4x5 field camera many years ago. So while it may be out of my budget presently, the thought of experimenting with it for those few dollars does look inviting.
[QUOTE=ray94553;491450] But a long lens tilt, I do wonder what that would be like.

The Pentax lens has NO TILT. It only provides shift!

Feel free to ask more to clarify things, looks all a bit confused.

Ben

02-17-2009, 12:34 AM   #77
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ray94553: For all those worried about my interpretation of crop factor. I've been corrected on this many times. But I think my way of saying is just fine
Ray, if your way of saying it were just fine, then you would not be corrected on it "many times."

It is this simple: the crop factor (Pentax DSLRs) is 1.5--300 X 1.5=450.
In order to get to 870mm, with a 300mm lens, you would need a crop factor of 2.9 since 2.9 X 300=870

Is this any clearer?

The crop factor (or FLM--focal length multiplier) is derived from the sensor's size relative to 35mm format's 24mm X 36mm. If the first several posts did not help, try this: Crop factor - Wikipedia, the free encyclopedia
02-21-2009, 08:45 AM   #78
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Caution: Adapter/lens lock problem

Got my adapter today and discovered that the 150mm f/2.8 won't lock on the adapter. Thing is, I don't think my copy of the adapter is faulty; the slot on the lens where the locking pin should drop into is displaced by about 10 degrees on the lens flange. If this adapter is a copy of the Pentax design, it's not sure that the real article would work any better.
02-21-2009, 02:05 PM   #79
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QuoteQuote:
baldeagle21b Caution: Adapter/lens lock problem

--------------------------------------------------------------------------------
Got my adapter today and discovered that the 150mm f/2.8 won't lock on the adapter. Thing is, I don't think my copy of the adapter is faulty; the slot on the lens where the locking pin should drop into is displaced by about 10 degrees on the lens flange. If this adapter is a copy of the Pentax design, it's not sure that the real article would work any better.
Which adapter did you buy? The one I have works beautifully on all my 67 lenses. If you post a shot of the adapter and the lens, I may be able to compare it ot my setup and see what is up.

02-21-2009, 02:33 PM   #80
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When using an MF lens on a crop dslr do you have to make any adjustment for aperature? , i.e. if there is not enough light to take a picture at f3.5 with a 35mm lens I assume there would not be enough light for the MF lens at f3.5.
02-21-2009, 03:46 PM   #81
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QuoteQuote:
spb37
When using an MF lens on a crop dslr do you have to make any adjustment for aperature? , i.e. if there is not enough light to take a picture at f3.5 with a 35mm lens I assume there would not be enough light for the MF lens at f3.5.
F 3.5 is f 3.5, on any lens, although there may be slight changes fom make to make. If there is not enough light to take a picture you can do 2 things: either you can decrease the shutter speed, or you can increase the ISO.

If you go back a page on this thread you will see 5 different %100 crops, taken with 5 different lenses. They are all shot at f8, with indoor, incandescent lighting. There is a Medium Format lens in that sample. If you look at those 5 samples, you will have the answer to your question.
02-21-2009, 07:24 PM   #82
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QuoteOriginally posted by Jewelltrail Quote
Which adapter did you buy? The one I have works beautifully on all my 67 lenses. If you post a shot of the adapter and the lens, I may be able to compare it ot my setup and see what is up.
I bought the same one you did, from the link you posted earlier in this thread. That's why I think the incompatibility is due to this particular lens.
02-21-2009, 08:32 PM   #83
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Can you post a picture of it, or a couple of pics, showing various angles?

02-22-2009, 07:49 AM   #84
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Hey ben !!!

Check this out:
Moveable digital back > 4x5 Camera > Pentax K200D K20D - eBay (item 200311095704 end time Feb-26-09 11:44:11 PST)
02-22-2009, 08:23 AM   #85
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QuoteOriginally posted by Jewelltrail Quote
Can you post a picture of it, or a couple of pics, showing various angles?
Here is a shot showing the problem. The combination is as tight as I can make it, but the pin and slot (position shown by the arrow) can't line up.https://www.pentaxforums.com/forums/attachments/10-pentax-slr-lens-discussion/28786d1235316028-medium-format-6-x-7-k20-sensor-imgp0151.jpg
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02-22-2009, 08:44 AM   #86
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I have bought this Widepan adapter, though from another, much cheaper reseller. It is nicely made, but the movement is more limited, than I had hoped for. I plan to give it a try during the second week of March, using it on my Graflex for some panos in the Alps.

Ben
02-22-2009, 10:00 AM   #87
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QuoteOriginally posted by baldeagle21b Quote
Here is a shot showing the problem. The combination is as tight as I can make it, but the pin and slot (position shown by the arrow) can't line up.
Quick and dirty shots of my 6x7 150mm and 105mm Takumars. I hope it can help you with your problem. Did your lens have the locking slot on the same position? If so, your adapter could be faulty.

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02-22-2009, 12:06 PM   #88
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QuoteOriginally posted by feverbeaver Quote
Quick and dirty shots of my 6x7 150mm and 105mm Takumars. I hope it can help you with your problem. Did your lens have the locking slot on the same position? If so, your adapter could be faulty.
Yes, my 150mm is exactly the same. I'll contact the seller this afternoon and ask for return information. Apparently my copy of the adapter is faulty. Thanks to everyone for your help.
02-22-2009, 12:36 PM   #89
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Yes, my 150mm is exactly the same. I'll contact the seller this afternoon and ask for return information. Apparently my copy of the adapter is faulty. Thanks to everyone for your help.
You may want to try this one thing first. After you align the 2 red dots be sure to hold the release pin mechanism on the adapter as you screw the lens and adapter together. Let me know if this works. Best of luck
02-23-2009, 04:24 PM   #90
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QuoteOriginally posted by Jewelltrail Quote
You may want to try this one thing first. After you align the 2 red dots be sure to hold the release pin mechanism on the adapter as you screw the lens and adapter together. Let me know if this works. Best of luck
Success! It took a little lubrication on the lens flange and a little more effort than I anticipated at first, but it works and the lens locks on to the adapter. Thanks to all for the suggestions.
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