focal length

flyer · 05-05-2010, 09:07 AM

Originally posted by Blue

It may be useless for the "average consumer." However, the crop factor or conversion factor or whatever you want to call it is used to calculate the fov or angle of view for a lens on one sensor or film size relative to a different one. This includes a 6x7 lens on a 24 x36 film body or aps-c sensor. It also applies to a 6 x7 lens on a 645 film camera or 645D version. So it has it purpose and utility. You don't even have to use the lens on 2 different film/senor sizes for this to have utility. For example, If I shoot an old abandoned church with a DA 21mm ltd on the K20d and want to replicate the shoot with the 6x7 on Portra NC, I won't be using a 21mm lens. What I have as wide angle for the 6x7 is a 55mm and 75mm. Which of those do you think will get me closer to the fov of the 21mm on APS-c from the same perspective?

(This is a real example I'm doing this week.)

Your point is valid as a conversion factor for a specific purpose, but for everyday shooting, you don't need a "crop factor" or conversion factor. You should know what you get with a given lens. If you want wide, you go for shorter than 30mm (on APS-C sensor), and longer than 30mm for telephoto.

The conversion factor is useful only for a few applications. Otherwise, people should forget about it.

When you change car, do you use a "crop factor" to see if it is larger or smaller than your previous car?

You don't. You just hop in and drive away.

enoeske · 05-05-2010, 09:11 AM

Originally posted by flyer

Your point is valid as a conversion factor for a specific purpose, but for everyday shooting, you don't need a "crop factor" or conversion factor. You should know what you get with a given lens. If you want wide, you go for shorter than 30mm (on APS-C sensor), and longer than 30mm for telephoto.

The conversion factor is useful only for a few applications. Otherwise, people should forget about it.

When you change car, do you use a "crop factor" to see if it is larger or smaller than your previous car?

You don't. You just hop in and drive away.

No but I do use a conversion factor when i go to canada and gas is sold in $/liter.

Blue · 05-05-2010, 09:13 AM

Originally posted by flyer

. . .
When you change car, do you use a "crop factor" to see if it is larger or smaller than your previous car?

You don't. You just hop in and drive away.

Actually, I don't have a car. It depends on where I'm going. If I'm towing a 22' camper or 12' enclosed cargo trailer I use my Bronco or Dually. Otherwise I use my Jeep.

I do look at gear ratios for the tranny and diff.

Class A · 05-05-2010, 03:04 PM

Originally posted by flyer

The conversion factor is useful only for a few applications.

That's a lot of progress compared to

Originally posted by flyer

The "crop factor" is absolutely useless.

Thanks for having kept an open mind.

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05-05-2010, 09:07 AM	#46
flyer Veteran Member Join Date: Jan 2008 Location: Ste-Anne des Plaines, Qc., Canada Posts: 2,013	Originally posted by Blue It may be useless for the "average consumer." However, the crop factor or conversion factor or whatever you want to call it is used to calculate the fov or angle of view for a lens on one sensor or film size relative to a different one. This includes a 6x7 lens on a 24 x36 film body or aps-c sensor. It also applies to a 6 x7 lens on a 645 film camera or 645D version. So it has it purpose and utility. You don't even have to use the lens on 2 different film/senor sizes for this to have utility. For example, If I shoot an old abandoned church with a DA 21mm ltd on the K20d and want to replicate the shoot with the 6x7 on Portra NC, I won't be using a 21mm lens. What I have as wide angle for the 6x7 is a 55mm and 75mm. Which of those do you think will get me closer to the fov of the 21mm on APS-c from the same perspective? (This is a real example I'm doing this week.) Your point is valid as a conversion factor for a specific purpose, but for everyday shooting, you don't need a "crop factor" or conversion factor. You should know what you get with a given lens. If you want wide, you go for shorter than 30mm (on APS-C sensor), and longer than 30mm for telephoto. The conversion factor is useful only for a few applications. Otherwise, people should forget about it. When you change car, do you use a "crop factor" to see if it is larger or smaller than your previous car? You don't. You just hop in and drive away.

05-05-2010, 09:11 AM	#47
enoeske Veteran Member Join Date: Jul 2009 Location: Surprise, Az Photos: Gallery Posts: 2,136	Originally posted by flyer Your point is valid as a conversion factor for a specific purpose, but for everyday shooting, you don't need a "crop factor" or conversion factor. You should know what you get with a given lens. If you want wide, you go for shorter than 30mm (on APS-C sensor), and longer than 30mm for telephoto. The conversion factor is useful only for a few applications. Otherwise, people should forget about it. When you change car, do you use a "crop factor" to see if it is larger or smaller than your previous car? You don't. You just hop in and drive away. No but I do use a conversion factor when i go to canada and gas is sold in $/liter.

05-05-2010, 09:13 AM	#48
Blue Moderator Site Supporter Join Date: Jun 2008 Location: Florida Hill Country Photos: Gallery \| Albums Posts: 17,377	Originally posted by flyer . . . When you change car, do you use a "crop factor" to see if it is larger or smaller than your previous car? You don't. You just hop in and drive away. Actually, I don't have a car. It depends on where I'm going. If I'm towing a 22' camper or 12' enclosed cargo trailer I use my Bronco or Dually. Otherwise I use my Jeep. I do look at gear ratios for the tranny and diff.

05-05-2010, 03:04 PM	#49
Class A Pentaxian Join Date: Aug 2008 Location: Wellington, New Zealand Posts: 11,251	Originally posted by flyer The conversion factor is useful only for a few applications. That's a lot of progress compared to Originally posted by flyer The "crop factor" is absolutely useless. Thanks for having kept an open mind.