300mm tube lens?

[JKT]

In the recent hunt for tube lenses and combinations the interest has been on short lenses. However, I'd like to know what are the known available and reasonably priced good quality choices for 300 mm tube lenses? Or at least tube lenses starting from 250 mm.

It seems to me that this would make sense when pairing quality optics with limited image circle to full frame camera with average pixel count.

[Lou Jost]

Yes, 300 and even 400mm tube lenses can be useful on FF. For 400mm I love the Nikon 400mm f/5.6 ED-IF. Not super cheap but old ones are a steal nowadays on eBay compared to their original price. The 300mm version is also pretty good but not as good as the 400mm version.

Medium format zooms by Pentax and Mamiya and S-K at their longest focal lengths can have very even quality across the frame, though they all do poorly at focal lengths significantly less than their maximum. Copy variation is huge in these.

The 250mm Precision Optics (Schneider) closeup lens is pretty good on APS, may be ok on FF, but I don't think I've tested it yet on FF. Maybe Robert has.

[Macrero]

I don't use infinity objectives at higher than nominal magnification, even on FF, but virtually any long FL enlarging/repro lens on bellows will do well enough. Long FL lenses tends to be more expensive, but still dirt cheap compared to other expensive options, and the difference (if any) would be trivial.

[Lou Jost]

"Nominal" only has meaning with respect to magnification, not FOV, so if you are happy with 200mm tube lenses on APS, you need a 300mm tube lens to get the same images on FF.

[Macrero]

"Nominal" only has meaning with respect to magnification, not FOV, so if you are happy with 200mm tube lenses on APS, you need a 300mm tube lens to get the same images on FF.

Or... I can use a higher mag objective with 200mm (or so) tube lens and get a similar FoV on FF.

I actually use 200mm (Mittys), 180mm (Olys) tube lenses only on FF. On APS and MFT I very rarely use tube lenses longer than 150mm.

[Lou Jost]

Or... I can use a higher mag objective with 200mm (or so) tube lens and get a similar FoV on FF.

Yes, that will often give you better image quality because of the higher NA of higher-powered objectives. But most of us have limited budgets and objectives are expensive compared to tube lenses. Best is to buy a high-m objective that can be pushed down with shorter tube lenses. But to make the most of our objectives, especially ones with small field numbers, it is very useful to use longer tube lenses, especially on FF.

You imply that you use 150mm tube lenses on MFT sometimes. Then using the same objective, you get exactly the same aerial image, with exactly the same quality, using a 300mm lens on FF.

You would get an even better image with a higher-powered, higher-NA objective and shorter tube lens, but only if the objective would fully cover FF (many do not).

[Macrero]

True enough. In that case using long FL tube lenses is a valid option. Though I would not call the 400mm f/5.6 ED a budget-friendly tube lens. For its price you can buy at least a couple of good used higher mag/res objectives to pair with your existing tube lenses. That's why I recommended enlarging/repro lenses, which are quality optics and can be found dirt cheap nowadays.

On MFT I actually like to push objectives down as much as possible. 150mm is the upper limit.

[Lou Jost]

I agree, pushing down is always better as long as coverage holds up.

I really like that 400mm Nikkor, it is perfectly apochromatic as a tube lens. And it is useful for general wildlife photography. I also prefer tube lenses with big front elements so they can be used on fast reversed camera lenses.

[JKT]

I think the Nikon is out, but Canon EF 300mm f/4 L with or without IS might be usable otherwise as well. Sadly FDN 300mm f/4 L doesn't have front filter threads ... or does it? FD 300mm f/4 S.S.C. has the same rear filter and no filter threads at front.

The mentioned Century Precision has also a big brother: +3.5 with 72 mm threads, which is a bit closer to target value. A bit expensive for testing, but if the +7 and +4 are good...

An alternate approach could be EOS M6 II, but apparently the AA filter spoils the theoretical equations. With RP and 300mm tube I should still be limited by camera resolution.

It will be interesting to see what the image circle actually is - the adapter hasn't arrived yet.

[rolsen]

I think Canon FDN 300/4 has 78,5mm front threads, at least regarding this conversation thread:
https://www.photo.net/discuss/threads/f ... 0-4.72841/

Apparently one must machine custom adapters

[JKT]

As mentioned at the bottom of the thread, it is actually not a thread at the end, but concentric rings. That makes the adapter even more problematic.

As I don't believe my FD 300 f/4 S.S.C. is good enough for the job, that route would be too complicated - and likely just as expensive - compared to either used EF 300 f/4 L or Century Precision +4 or +3.5.

There are plenty of used 300mm f/5.6 lenses available for next to nothing, but the quality likely matches the price.

[zed]

While I normally appreciate the experimentation that takes place here on this forum - this is one that doesn’t make sense to me. Mainly because I cannot think of a practical reason why using a tube lens with a focal length longer than what the objective was designed for helps improve image quality. Using a slightly shorter focal length helps because we all use cameras with sensor resolutions that mostly exceed the objective’s resolving power - so for a given NA reducing the magnification assists the fixed sampling frequency of our cameras.

Increasing magnification without increasing NA hurts your image quality more than it helps. It might handle chromatic aberrations OK, but it will certainly enhance spherical aberrations more that you would like which will reduce both perceived sharpness and contrast. And with the extremely wide variety of appropriate focal length tube lens options that many forum members have ferreted out (not many better than the cheap Raynox DCR-150) you would be much better off using a tube lens with a slightly shorter focal length coupled with a higher mag PLUS higher NA objective.

Just keep in mind that this 'improvement' you are seeing by shortening the focal length of the tube lens is mostly due to getting a closer match of the resolving power of the objective to the sensor resolution of the camera. See Nyquist.

For example, if I have a specimen that needs to be imaged at slightly higher than 10X - say 15X, I would much rather use a 20X/0.42 objective with my Raynox at 150mm vs a 10X/0.28 with a 300mm tube lens. The image quality on a FF would be night and day in favor of the Raynox.

And finally - can you imagine mounting a 400mm lens plus camera and objective to any focus mechanism (Stackshot or microscope drive)? The anchor point for these devices are very small - and even if your setup is properly isolated this would be a vibration nightmare.

[Lou Jost]

I cannot think of a practical reason why using a tube lens with a focal length longer than what the objective was designed for helps improve image quality.

In a previous comment I just gave such a case. I'll say it again: If you are pleased with an image with a given objective and 200mm tube lens on an APS sensor, you get EXACTLY THE SAME AERIAL IMAGE if you use a 300mm lens on a FF sensor. But now you've put more pixels beneath the aerial image. So the image will be better (or at least not worse) than the APS version with the 200mm tube lens.

Of course its even better to buy a more powerful objective with a higher NA. But that's not always an option for some of us.

Furthermore, many objectives don't cover a FF sensor well in the corners when using a 200mm tube lens. A 300mm tube lens will fix that nicely.

In addition, there are some objectives which have high NA and which can stand being pushed up with little or no loss of image quality. A good example is the cheap 20x 0.70 Nikon Apo, which costs almost nothing now.

Using a 300mm or 400mm tube lens is no harder for me than a shorter focal length. I use a microscope block controlled by a WeMacro MicroMate. I use a vertical system with the front of the tube lens sitting on the focusing stage. Fairly solid.

[Lou Jost]

I think for FF it is quite reasonable to use a 250mm lens as the default length of tube lens. Most people are happy with using a 180-200mm tube lens on APS. Their FF images with a 250mm tube lens will be better than their APS images with a 200mm tube lens, if their objective has a wide enough image circle. If not, then they should use a 300mm tube lens.

Or, of course, buy a new objective with higher NA and higher field number.

[JH]

On my Optiphot microscope I use these lenses above 200mm
Nikkor 300mm 4.5
Apo Ronar 360mm 9
Canon 400mm 5.6

Using a longer tube lens enlarges the image circle. Say that a Nikon microscope objective have a 25mm good image circle, and your FF sensor have a 43mm diagonal (sqrt (24^2+36^2)). To cover 43mm you need a 344mm (200*(43/25)) tube lens.

For subjects where the corners do not matter but I want to capture as much detail as possible I also want to use a longer tube lens if the objective out resolves my camera sensor. Just now I am testing a Nikon 20x NA 0.75 infinity objective that out resolves my sensor.

Best regards
Jörgen Hellberg