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Old 14-06-2008, 12:05 PM
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dugnsuz (Doug)
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ED80 and DSLR 1.6x crop factor

Hello all,
Just a quickie!
As with lenses, could anyone confirm that the 1.6x crop on DSLRs like my 40D would be there with a scope (ED80 for example)?

In effect the 600mm FL of the ED80 would be 960mm!!??

Is that correct?

Cheers in advance

Doug
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Old 14-06-2008, 12:09 PM
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Terry B
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Quote:
Originally Posted by dugnsuz View Post
Hello all,
Just a quickie!
As with lenses, could anyone confirm that the 1.6x crop on DSLRs like my 40D would be there with a scope (ED80 for example)?

In effect the 600mm FL of the ED80 would be 960mm!!??

Is that correct?

Cheers in advance

Doug
Not really.
The 1.6X crop is referring to a 35mm film frame and compared to this it would be a 1.6x crop but I don't think the ED80 would fill a 35mm frame without lots of vignetting. Anyone tried it?
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Old 14-06-2008, 03:42 PM
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The question is wrong.. But the answer to right question ("What is the scale of 600mm lens") would be:
600mm lens has a scale of 1.96arcsec/pixel (if pixel size is 5.7um)
Or. it will have the field of view 53.7x35,8 arc min with 400D (I think this is the same as 40D)

Edit:
This crop factor business is here only because the DSLR's sensors are usually smaller than SLR film size, and people want to compare things....
So any given lens on 35mm camera obviously will have (1.6x in case od 22x14mm sensor) wider field of view, compared with DSLR's with smaller sensors.

Last edited by bojan; 14-06-2008 at 04:06 PM.
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Old 14-06-2008, 06:53 PM
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dugnsuz (Doug)
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Quote:
Originally Posted by bojan View Post
This crop factor business is here only because the DSLR's sensors are usually smaller than SLR film size, and people want to compare things....
So any given lens on 35mm camera obviously will have (1.6x in case od 22x14mm sensor) wider field of view, compared with DSLR's with smaller sensors.
Got it!
Thanks.
Doug
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Old 19-06-2008, 10:01 PM
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Dougie

When I brought the Pentax and told the guys I had lens from a SLR they said that I need to mutiply their FL by 1.5 so a 300mm lens in the equivalent of a 450mm lens on a DSLR.

Apparently a DSLR CCD is the equivalent of a 26mm film size or something.

Is this the same thing
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Old 20-06-2008, 03:58 AM
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iceman (Mike)
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Yes, Trevor. That's right.

That's the "crop factor" at work.

Not so bad when you want the long focal length, but makes it very hard to get a nice wide angle/fish eye lens.
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Old 20-06-2008, 09:12 AM
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"Crop Factor" term should be banned, at least in astrophotography, because it is misleading and confusing, and quite meaningless.
Use scale (arc sec/ pixel) or view field for particular sensor/lens combination (arc sec, vert x horizontal or diagonal).
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