A finder for the 75mm?

T

Terao

Kiloran
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Does such a thing exist? There only seem to be D finders for the wides. As an approximation would using the 50mm framelines as a guide be sufficient?
 
why not get an old 50mm accessory finder?

or, if you can't find a s/h one, CV make one, Robert White are charging 85 + VAT for it.
 
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75mm lenses have a 115mm FoV on the R-D1.
A 90mm or 135mm finder could to the trick perhaps.
Best,
LCT
 
Terao said:
Does such a thing exist? There only seem to be D finders for the wides. As an approximation would using the 50mm framelines as a guide be sufficient?
Click to expand...

Hmm, lessee...

Focal length: 75mm

Conversion factor for 35mm-format finders: 1.53x

Parallax compensation safety factor (the one Epson designed into its finder frames to allow for the fact that effective focal length increases as you focus closer): 85%.

So:

(75*1.53)/0.85 = 135, meaning an accessory viewfinder meant for a 135mm lens on a 35mm camera should be a good match for a 75mm lens on the R-D 1.

In practice, "your mileage may vary," because the manufacturers of accessory finders also incorporated a parallax compensation safety factor, and this differs from one manufacturer to another. For example, I've got a Canon 135 finder that happens to match up pretty well for using a 100mm lens on my R-D 1, even though in theory this finder should be a bit too "loose." Apparently Canon designed a rather generous safety factor into this finder's framelines.

If you decide to accept the finder's safety factor, you can omit the 85% safety factor for the above calculation. Then you wind up needing about a 115mm finder -- good luck finding one of those!
 
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jlw said:
...Parallax compensation safety factor (the one Epson designed into its finder frames to allow for the fact that effective focal length increases as you focus closer): 85%. So: (75*1.53)/0.85 = 135...
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If you want to introduce a 0.85x parallax compensation factor should not you multiply instead of divide by 0.85?
75*1.53*0.85 = 98mm
Just curious.
Best,
LCT
 
LCT said:
If you want to introduce a 0.85x parallax compensation factor should not you multiply instead of divide by 0.85?
75*1.53*0.85 = 98mm
Just curious.
Best,
LCT
Click to expand...

I know, it can be VERY confusing and I'm never sure I'm doing it right when I whip out these quickie answers!

So, let me run through my thinking and you can decide whether or not it checks out:

75 * 1.53 "35mm correction factor" = 114.75. So, if you omitted the safety factor, you'd need a 115mm finder. I'll call this 115mm number the nominal value.

To provide the safety factor, you want to make your finder frame smaller -- so that the final image will always contain at least as much as you saw through the finder, even when the effective focal length increases as you focus closer.

To do that, you need to choose a finder for a focal length that is longer than the nominal value.

If you were to multiply the nominal value by 85%, you'd be making your focal length shorter and your frameline wider: 115 x 0.85 = 97.75mm, as in the example above. But... wider is NOT the direction you want to go.

To make your focal length longer and your frameline tighter, you DIVIDE the nominal value by the 85% safety factor: 115 / 0.85 = 135.3mm.

This frameline equivalent should give you a small enough field of view that there's always more image than you saw through the finder, even when you're at closest focusing distance.

Make sense? I'm certainly not immune to bonehead math errors, so if this rationale sounds goofy, feel free to propose corrections.
 
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Yes. The closest accessory finder would probably be a Nikon one for the 105/2.5 Nikkor-P, but I find it easier to just imagine 75mm frames inside the 50mm (just like on an M Leica) close up & the 50mm frames themselves @ infinity ;)

Terao said:
So, in summary, approximate using the 50mm framelines in the R-D1's finder :D
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The 50mm framelines will be much too "loose" to even roughly approximate the field of view of a 75mm lens. That's why pfogle and I were expending our brainpower recalling our grade-school arithmetic skills, to tell you what finder would roughly approximate it.

But if you can imagine 75mm coverage inside a 50mm frameline, go for it. Heck, if your imagination is that good, why bother with a viewfinder at all?
 
I just got my R-D1 today. You guys have my head spinning with this post. Could someone please clarify which was the correct explanation. I have a 75mm on my list to purchase.
 
Cindy Flood said:
I just got my R-D1 today. You guys have my head spinning with this post. Could someone please clarify which was the correct explanation. I have a 75mm on my list to purchase.
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My post had all the correct math. It shows that for a 75mm lens on an R-D 1, you should first try a viewfinder made for using a 135mm lens on a 35mm camera. If a 135mm finder is consistently too "tight" (shows too little of the final image) then you might try a 100mm or 105mm finder instead.

It's impossible to be more specific because different manufacturers designed their finders with slightly different areas of coverage. Fortunately, the R-D 1 makes it easy to shoot test photos and compare the final image with the finder coverage. For the most accurate results, shoot your test photos at the closest distance you routinely shoot -- framing is more critical at close distances.


That's the simplified answer. Skip this next part if you don't want a lot of extra detail:

The reason we couldn't just give you a flat answer is that this question isn't as clear-cut as you might think -- it's not just a simple mathematical conversion. There are three factors at work that make it tricky:

-- A lens actually "zooms in" slightly as you focus closer; that means that a viewfinder that perfectly covered the lens' field of view at infinity would show too wide a view at close distances. If you composed right out to the edge of that wider view, you'd be disappointed to find that some objects you had expected to be included were cropped out of the final picture.

-- To compensate for this zoom-in effect, a finder is usually designed with a "safety factor", causing it to show a slightly "tight" field at normal distances. This assures that everything you see through the finder will be in the final picture, regardless of distance.

-- But, different manufacturers choose slightly different safety factors. Epson uses 85%; others may be a bit more or less.

These three variables are why we can't just arbitrarily say "Use finder X for lens Y." It depends a bit on the specific lens, the specific brand of finder, and whether you normally shoot close-up or at a distance.

Sorry if this makes it seem confusing again, but I wanted to make sure you knew we weren't just yanking your chain.
 
Thank you for the clarification. I just wanted to make sure that I understood the math concerning the 85% (multiply or divide). That is where it became confusing. I do understand the zoom-in effect and the 1.5x conversion.
 
Cindy Flood said:
Thank you for the clarification. I just wanted to make sure that I understood the math concerning the 85% (multiply or divide). That is where it became confusing. I do understand the zoom-in effect and the 1.5x conversion.
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Don't feel bad. All this crop factor and frameline conversion stuff can drive a person crazy. If its any consolation, just try out the lenses you have and try different framelines that Epson provides in the camera. whichever one fits how you want the lens to frame, is the right one. Personally, I would try using the center of the 50mm frame for the 75mm lens before spring for a $175 finder.

The only finder I would buy would be for a lens that is wider than any frameline in the RD1 viewfinder. For that the VC 28-35mm minifinder works great. I have about 7 finders of various FL and if I had to do it over again I'd just get the mini-finder and forget the rest. But you don't have a wide yet so forget it .

Rex
 
Cindy Flood said:
Thank you for the clarification. I just wanted to make sure that I understood the math concerning the 85% (multiply or divide). That is where it became confusing. I do understand the zoom-in effect and the 1.5x conversion.
Click to expand...

Don't feel bad. All this crop factor and frameline conversion stuff can drive a person crazy. If its any consolation, just try out the lenses you have and try different framelines that Epson provides in the camera. whichever one fits how you want the lens to frame, is the right one. Personally, I would try using the center of the 50mm frame for the 75mm lens before spring for a $175 finder.

The only finder I would buy would be for a lens that is wider than any frameline in the RD1 viewfinder. For that the VC 28-35mm minifinder works great. I have about 7 finders of various FL and if I had to do it over again I'd just get the mini-finder and forget the rest. But you don't have a wide yet so forget it .

Rex
 
Cindy Flood said:
Thank you for the clarification. I just wanted to make sure that I understood the math concerning the 85% (multiply or divide). That is where it became confusing. I do understand the zoom-in effect and the 1.5x conversion.
Click to expand...
sorry for the confusion - you wouldn't think I've got a math degree, would you? :eek:
 
Use an old imarect from Leica. It is coontinuously variable. I marked mine for 40 mm, 75, and some other oddballs.

It is very accurate, but the image is uncoated glass and poor.

Match it what is on the digi fiile with the 75.
 
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