Question about using Nikkor M 300m f9 on an Ebony 45S

[duff photographer]

Hello!

I recently acquired a Nikkor M 300mm f9 and want to know the 'range' of focus on an Ebony 45S (with appropriate extended lensboard).

The 45S extends 270mm while the lens has a backflange of 290mm. I intend to use a 35mm top hat/extended lensboard so this will give me 15mm to play with. However, while the lens will focus at infinity with the top hat I don't know what the minimum focusing distance would be. I don't want to buy the lensboard and waste my money if the minimum focusing distance is still miles away so would anyone know what the minimum focusing distance would be?

Many thanks.

:-)

[Larry Gebhardt]

I don't remember the calculation, but when I had a Shen Hao with 360mm of extension I was able to use that lens without much issue as far as extension went. There were a few times I wanted to focus closer, but it worked well enough for most shots. I think you will not be happy with only 35mm of additional extension.

[Kirk Fry]

Just buy a Calumet CC401 for $100 and be done with it.

[Doremus Scudder]

With that little extension, you will really only be able to work at infinity, since most subjects have some foreground objects in them that require splitting the focus distance, and since the lens has a rather shallow depth of field for 4x5. You will likely want a top-hat board with more extension than that. I use mine on a Wista DX with 300mm of extension; my board is about 30mm of extension (giving me 40mm to "play with") and I can't really do anything that resembles a close up. Nine meters is about closest focus.

Once you have a board with enough extension in hand, you'll find that the 300mm M is a sweet lens and very sharp. Or, you can acquire the Ebony extension back :)

Best,

Doremus

[dave_whatever]

Hello!

I recently acquired a Nikkor M 300mm f9 and want to know the 'range' of focus on an Ebony 45S (with appropriate extended lensboard).

The 45S extends 270mm while the lens has a backflange of 290mm. I intend to use a 35mm top hat/extended lensboard so this will give me 15mm to play with. However, while the lens will focus at infinity with the top hat I don't know what the minimum focusing distance would be. I don't want to buy the lensboard and waste my money if the minimum focusing distance is still miles away so would anyone know what the minimum focusing distance would be?

Many thanks.

:-)

By my calculations, just inside 6m will be about the limit.

[duff photographer]

Thanks Larry, Doremus and Dave.

Looks like I'll need a lot more extension than is practical for the camera.

I did think about the Ebony extension back but the cost and extra bulk has put me off. I'll just use the lens for my MF digital work - and yes, it is very sharp isn't it :-) .

Out of curiosity and a wont for understanding, how does one calculate the focusing range of a LF lens (forgive my ignorance on this one)?

Cheers!

[dave_whatever]

If you google "thin lens formula" that will give you the idea.

[duff photographer]

If you google "thin lens formula" that will give you the idea.

Done, and many thanks for helping me increase my knowledge base.

:-)

[drew.saunders]

Hello!

I recently acquired a Nikkor M 300mm f9 and want to know the 'range' of focus on an Ebony 45S (with appropriate extended lensboard).

The 45S extends 270mm while the lens has a backflange of 290mm. I intend to use a 35mm top hat/extended lensboard so this will give me 15mm to play with. However, while the lens will focus at infinity with the top hat I don't know what the minimum focusing distance would be. I don't want to buy the lensboard and waste my money if the minimum focusing distance is still miles away so would anyone know what the minimum focusing distance would be?

Many thanks.

:-)

The 290mm flange focal distance of the lens gives you a 10mm "free top hat," so you do the calculations as if you had a 270mm + 35mm + 10mm extension, for 315mm of extension.

1/focal length - 1/extension = 1/subject distance
1/300 - 1/315 = 1/6300

So you can work to 6.3m or thereabouts. Not ideal, but still useful if you only want that lens for fairly distant subjects. The Fuji 300/8.5 has a 282.3mm flange focal distance, so you'd end up with a 4.4m or so minimum distance with that lens, for example. I bought the Fuji over the Nikkor when I had a Tachihara just to eke out that extra close focusing.

[duff photographer]

The 290mm flange focal distance of the lens gives you a 10mm "free top hat," so you do the calculations as if you had a 270mm + 35mm + 10mm extension, for 315mm of extension.

1/focal length - 1/extension = 1/subject distance
1/300 - 1/315 = 1/6300

So you can work to 6.3m or thereabouts. Not ideal, but still useful if you only want that lens for fairly distant subjects. The Fuji 300/8.5 has a 282.3mm flange focal distance, so you'd end up with a 4.4m or so minimum distance with that lens, for example. I bought the Fuji over the Nikkor when I had a Tachihara just to eke out that extra close focusing.

Thanks. I understood that, and the trick is not to round the figures up too much:

What sort of lenses does this actually work on? I ask that because my Schneider 400mm f5.6 A-T-X Comp (which I use with the 35mm top hat) makes a mockery of the calculation (sadly).

1/focal length - 1/extension = 1/subject distance

1 divided by focal length = 1/400mm
1 divided by extension = 1/315mm

Subject distance = 0.002500mm - 0.003175mm

= -0.000675mm

1/-0.000675mm

= -1481mm (-1.5 metres)


The negative number is obviously wrong but of course the lens is a telephoto design. Therefore, would it be better to replace the focal length in the calculation with the back flange distance? In this case it would be 285mm for the 400mm.

This would make the calculation...

1 divided by back flange (at infinity) = 1/285mm
1 divided by extension = 1/315mm

Subject distance = 0.003509mm - 0.003175mm

= 0.000334mm

1/0.000334mm

= 2992mm (3.0 metres)

However, when I field tested it, it was in the 6.5 to 7 metre range (aperture wide open)! I'm guessing the equation doesn't work for this type of lens?

Assuming the use of the back flange figure instead of the focal length may be better way of calculating distance for non-telephoto designs, the 300mm (with its 290mm backflange) comes out at 3.7 metres. Would this be why your Fuji was a better bet than the Nikkor due to its shorter backflange? Sorry, if I'm missing something obvious :-)

By the way, thanks for making my brain work :-D

Cheers
DP


PS. I see that a 45mm top hat will give me 2.7 metres which suggests the Nikkor 300mm lens is very workable in the field, even if, alternatively, the focal length was used in the calculation. However, I'm getting the impression there's more to this than I've simplified and I would love to be corrected if I'm wrong.

[BradS]

Thanks. I understood that, and the trick is not to round the figures up too much:

What sort of lenses does this actually work on? I ask that because my Schneider 400mm f5.6 A-T-X Comp (which I use with the 35mm top hat) makes a mockery of the calculation (sadly).

1/focal length - 1/extension = 1/subject distance

1 divided by focal length = 1/400mm
1 divided by extension = 1/315mm

Subject distance = 0.002500mm - 0.003175mm

= -0.000675mm

1/-0.000675mm

= -1481mm (-1.5 metres)


The negative number is obviously wrong .

No. the negative number is telling you that you cannot focus a lens with fl = 400mm with only 315mm of bellows.



but of course the lens is a telephoto design. Therefore, would it be better to replace the focal length in the calculation with the back flange distance? In this case it would be 285mm for the 400mm.



The focal length is actually the distance from the rear nodal point of th lens to the plane of focus when the lens is focused at infinity. We can simplify this a little for non-telephoto lens designed. In LF, this is most all lenses ase few are actually telephoto designs. The 300mm Nikkor-M for example, is a fairly pedestrian tessar type...completely normal. And so, the usual approximations apply - that is, we approximate the position of rear nodal point to be roughly in the plane as the flange (ie, the lens board). Thus we approximate the focal lengh with the flange focal length....but, this ONLY works for lenes of "normal design".

If your 400 mm lens is in fact a telephoto, then it is pretty much guaranteed that the focal length is considerable longer than the flange focal length (that's the whole point).

Make sense?

[duff photographer]

No. the negative number is telling you that you cannot focus a lens with fl = 400mm with only 315mm of bellows.

Yep, I worded it badly. The calculation was correct but meant to say it was not applicable to the 400mm being a telephoto.





The focal length is actually the distance from the rear nodal point of th lens to the plane of focus when the lens is focused at infinity. We can simplify this a little for non-telephoto lens designed. In LF, this is most all lenses ase few are actually telephoto designs. The 300mm Nikkor-M for example, is a fairly pedestrian tessar type...completely normal. And so, the usual approximations apply - that is, we approximate the position of rear nodal point to be roughly in the plane as the flange (ie, the lens board). Thus we approximate the focal lengh with the flange focal length....but, this ONLY works for lenes of "normal design".

If your 400 mm lens is in fact a telephoto, then it is pretty much guaranteed that the focal length is considerable longer than the flange focal length (that's the whole point).

Make sense?

Yep. :-)

Many thanks.