Little view camera lens question

[Paul Spinnler]

Hi guys!

I just have a small question regarding view camera lenses. According to the specifications, the new Schneider 43 XL has an image circle of 110 mm at f 11.

When talking about focal lengths of view camera lenses, does the 43mm designation refer to the field of view when using the whole image circle or only when using a medium format the diameter of 645 full frame?

I.e., can i get an effective focal length of 28 mm medium format lens with the 43 XL when fully stitching with say a P65+ or does the effective focal length of a fully stitched image equal 43 mm in medium format terms?

Sorry if my question seems confused, but I must confess that I'm a newbie to this matter and hence do not fully comprehend all what's involved in these many focal length calculations ...

Regards

Paul

 

[thomas]

in short...

I.e., can i get an effective focal length of 28 mm medium format lens with the 43 XL when fully stitching with say a P65+

... yes.

 

[smei_ch]

in short... ... yes.

In short: no. The lens always has 43mm focal length. How much you get out of the offered image angles with the image circle of 110mm in comparison to a 28mm on a DSLR depends on how you stitch.

Simple Pythagoras. This might help too: http://m.alpa.ch/dms/downloads/tools/ALPA_CFL_Calc_V217B.xls

 

[Jack]

Or stated another way,

A 43mm lens is a 43mm lens regardless of what camera you mount it on. What will change is the frame size of the camera, and thus 43mm focals will render differently with different frame sizes, eg to the effective focal for that format. So 43mm on a P65+ is roughly equivalent to 43mm x .64 focal factor = 27.5mm effective. Thus, using the 43 with a P65+ back will effectively render a similar framing to using a 28mm lens on full frame 35 cameras.

The howeverbutt caveat is due to the difference in aspect ratios between the P65+ and FF 35mm...

 

[thomas]

The lens always has 43mm focal length.

of course you can't change the focal lenght of a lens. But if you re-read the initial post you may find that the simplified answer to the simplified question I quoted is indeed "yes": the 43XL without movements will act like a 45mm lens (at least very similar in terms of image circle) on a 645 camera. And that is what Paul wanted to know... unless I get the qustion completely wrong.
-> can i get an effective focal length of 28 mm medium format lens with the 43 XL when fully stitching with say a P65+ or does the effective focal length of a fully stitched image equal 43 mm in medium format terms?

 

[H3dtogo]

i always tought a 43mm on a P65 stays simply a 43mm...... unless you stitch.

 

[Jack]

of course you can't change the focal lenght of a lens. But if you re-read the initial post you may find that the simplified answer to the simplified question I quoted is indeed "yes": the 43XL without movements will act like a 45mm lens (at least very similar in terms of image circle) on a 645 camera. And that is what Paul wanted to know... unless I get the qustion completely wrong.
-> can i get an effective focal length of 28 mm medium format lens with the 43 XL when fully stitching with say a P65+ or does the effective focal length of a fully stitched image equal 43 mm in medium format terms?

Perhaps the wording is the issue. If he wants an effective 28 FoV in full-frame 35mm terms, he doesn't have to stitch as the 43 is already there. However, if he wants to get to get a 28mm MF FoV using the 45, then he has to stitch to get the P65+'s 67.2mm diagonal proportionately larger up to 103.2mm --- IOW capture roughly a 62x83 frame if he wants to keep a 3:4 aspect ratio. Since the lens has a 110mm IC, he's good to go with a few mm to spare .

 

[thomas]

Perhaps the wording is the issue.

I agree...

if he wants to get to get a 28mm MF FoV using the 45, then he has to stitch to get the P65+'s 67.2mm diagonal proportionately larger up to 103.2mm.

exactly.
Without stitching the 43mm lens is a 43mm lens. With stitching the 43mm lens is still a 43mm lens but due to the movements the field of view gets wider ... i.e. it equals the field of view of a wider lens on the given film format. Of course stitching does not change the focal length... but stitching enlarges the film format.

 

[Paul Spinnler]

Hi guys! Thank you for your responses - for me it is really hard to formulate this question accurately since German is my mother tongue and not English.

I just wanted to know about the effective field of view I could get out of a 43 XL when using the full image circle by way of stitching.

So as I gather from the responses, when using the complete image circle, I still will have a 43mm focal length lens but with effectively a larger then 645 film format which in turn will give me an effective field of view of an 28mm lens such as the 28 mm HC 4.0 on the H4D-60.

Concluding, the 43 XL corresponds to:

a 28mm in 645 film format when using the 110 IC which in turn corresponds to
a 18mm lens in 35mm film format -> which is really wide!

I wanted to know about this because I was wondering whether the 43 XL would be a good all around lens choice for architectural photography considering that I have a limited budget of one lens to start my view camera endeavors with.

Would you guys agree that the 43 XL is indeed a very useful starting lens, especially considering the huge sensor (H4D-60) I ordered?

Also, am I right that by doing a 4 image stitch to get all out of the 110 image circle I will aproximately get a 95 MP image?

Regards

Paul

 

[thomas]

I think I just copy/paste what I've written in another thread some days ago:

As to the image plane and lens factor just add the amount of movements to your sensor plane and devide the diagonals of the resulting image planes to find the lens factor.
So your P65+ sensor is 53.9 x 40.4 mm. The diagonal is 67.4 mm.
If you add movements of, say, 10mm rise/fall and 10mm left/right you are working with an image plane of 73.9 x 60.4 mm. The diagonal = 95.4 mm.
So with 4 way movements of 10mm the lens factor is 1.4.
Therefore a 40mm lens translates to the field of view of a 28 mm lens.
If you take the image format into account (i.e. 4:3, 5:4, 3:2 …) the lens factor will vary.

You have to take sharpness falloff into account. With large movements the edges go soft... significantly. On the other hand you gain resolution and you'll have to evaluate that trade off. Those 95MP therefore are a bit theoretical... as at the edges you are working with half the resolution or even less (due to the falloff).

Is the 43XL already available? It was anounced to be released sometime this spring/summer but I haven't heard that it is already shipping...

I use the 47XL. I'd say it's a perfect allrounder lens... if you can just afford one lens I'd take the 47XL resp. 43XL.
This goes for the 47XL: you have to use it at f11 or f16, especially when stitching. f8 is fine but it'll show some falloff even without movements (the 43XL is supposed to be better here). It shows very little distortion (the 43XL is supposed to be even better here) but the distortion is very easy to correct as it is totally linear ("Alpa Lens Corrector" does a very nice job).
It easily covers the respective field of view of a 35mm lens when stitching (in this case without suffering from soft edges). However note that stitching is not always an option (changing light or whatever...).
With the 47XL you'll need either a centerfilter or do multiple exposure as light falloff with large movements is significant.

 

[Jack]

Also, am I right that by doing a 4 image stitch to get all out of the 110 image circle I will aproximately get a 95 MP image?

Regards

Paul

First point is that if you use the full 110 IC, you'll have closer to a 26mm effective FoV, or a 17mm in 35 terms. Second is that since you are increasing the DIAGONAL of your P65+ sensor area by roughly 1.64x, you are actually increasing the AREA by about 2.69x, so you will end up with a total capture area of around 160MP!

 

[Paul Spinnler]

@Thomas: I talked to Cambo today and they said that the lens would be sourceable from Schneider within the next 2 weeks but that they needed another month or so to adapt it to the Cambo mount. So the prediction for availability is now between 6-7 weeks ...

@Jack: If you have a 110 mm IC, in your experience, how much of this IC will be really sharp? Comparing to your 47 XL for example, if you have utmost desire for corner sharpness, how much are you willing to shift? Up to 90mm? 100mm?

Regards

Paul

 

[thomas]

...so you will end up with a total capture area of around 160MP!

uhh, right! I didn't recalculate (or at least thought about) the resulting resolution...

 

[Arjuna]

"Concluding, the 43 XL corresponds to:

a 28mm in 645 film format when using the 110 IC which in turn corresponds to
a 18mm lens in 35mm film format -> which is really wide!"

Not exactly, unless you are referring to the stitched case. I think that a 28 mm lens on 35 mm format has a horizontal angle of view of 65 degrees, which corresponds to about a 44 mm lens on 645 / 6x6 format (i.e. about 56 mm wide), so the 43XL on a practically full width sensor is pretty much equivalent to a 28 mm efov (35 mm format). I prefer to use horizontal angles of view for equivalences, as I don't shoot many pictures on a diagonal.

In your original post, when you said "I.e., can i get an effective focal length of 28 mm medium format lens", I think some people interpreted it as 28 mm in 35 mm terms, since, in medium format terms, the 43 is a 43, single shot. So I think that the original question could be re-stated as; given the image circle of the 43XL, if you do a stitch, do you end up with a picture that has the same (horizontal) angle of view (but different aspect ratio), as if you had used a 28 mm (medium format) lens? and the answer seems to be a qualified yes.

 

[thomas]

how much of this IC will be really sharp?

this may help: http://forum.getdpi.com/gallery/showimage.php?i=5177&original=1
For me... up to 17mm shift...
But the sensor of the H4D60 is already 5mm wider... so you have to deduct that from the amount of usable movements... assuming that the lenses work identically on both the sensors.

edit: 17mm lateral in landscape mode resp. 17mm rise or fall in vertical composition. So 34mm altogether.
note: 34mm lateral or vertical... not diagonal (i.e. not 17mm lateral and 17mm vertical at the same time)

 

[Jack]

@Jack: If you have a 110 mm IC, in your experience, how much of this IC will be really sharp? Comparing to your 47 XL for example, if you have utmost desire for corner sharpness, how much are you willing to shift? Up to 90mm? 100mm?

Regards

Paul

Hi Paul:

It's tough to say until we hear from users of the actual lens -- or at least we can look at an MTF chart. IC's from Schneider and Rodenstock for the latest generations of digital lenses are generally reasonable to slightly conservative. So I would suspect the total IC will be "usable" to some definition -- the lens may well illuminate beyond 110mm. Here is also one area where stopping down can help -- yes, diffraction increases, but usually at a lesser rate than edge performance improves, so you may actually find more usable IC for your purposes, depending...

At the end of the day, I would be pretty confident saying that if you stay inside say 80% of the IC, or the central 88mm, you'll probably be very happy with the results