12 replies to this topic

[The Ardent]

Finally got all the pieces together: large aperture lens, adapter, mounting rings and plate, filter. 

 

The goal: observe M8 and M20 the final time this year. 

 

Rersults: Success! And failure. 

 

This is is the Canon 300 2.8 FD L telephoto found used. It's probably older than me. It's a very heavy lens. Requires solid mounting. Shown here with 125mm ADM rings and Losmandy plate. 

 

Features a rear 48mm filter holder. Normal astro 2" filters thread into it, but the filter cells are too wide to fit in the slot. The Canon filters made for these lenses have low-profile cells. The solution last night was to remove the filter from the cell. The glass simply press-fits into the Canon holder. Not too tight- don't want a broken or cracked filter. A filter under stress will probably distort the star images too. 

The other solution is a four-inch H-alpha filter, but that ain't happening. 

 

The waxing crescent moon was only a few degrees west of M8. The lens frames M8 and M20-21 in the same FOV. The filter is easily removed/replaced for different targets. I swept up the Milky Way to M24, M18, and the grand sights of M17 and M16. 

 

After an hour or so the lens adapter fell apart. I switched to a different lens. Happy that the Canon lens works well for NV. Disappointed that our time was cut short. 

 

For NV the lens exists somewhere between handheld observing and telescopic. It can be handheld for quick looks. It's very heavy. A small telescope is better in many respects (zenith viewing , focus lock for example ) 

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[Jeff Morgan]

What an awesome lens!

 

Setting up a 3.6 degree circle and panning over the Milky Way in SkySafari, the possibilities are mouth-watering.

 

Might even be worth building a bino-chair to solve the stability and neck-craning issues.

[The Ardent]

Here is M8 and M20 from last night. Unfiltered, single handheld iPhone photo. These were close to the horizon , and interference from the waxing crescent moon.

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[GeezerGazer]

Features a rear 48mm filter holder. Normal astro 2" filters thread into it, but the filter cells are too wide to fit in the slot. The Canon filters made for these lenses have low-profile cells. The solution last night was to remove the filter from the cell. The glass simply press-fits into the Canon holder. Not too tight- don't want a broken or cracked filter. A filter under stress will probably distort the star images too. 

The other solution is a four-inch H-alpha filter, but that ain't happening. 

 

Ray,

Using my Nikon 300mm f:2.8, I found a way to use 1.25" filters quite successfully.  The Nikon has a 39mm filter holder built in like your 48mm filter holder... I too simply removed the UV filter that came installed.  I purchased an inexpensive bayonet mount to m42 (TT) thread and use a filter retaining ring with a ScopeStuff C2TT adapter.  If the Cannon lens has enough back focus to accommodate these accessories, you should find it works fine for NV H-a imaging.  Here's a link to how it looks and what parts I used to allow successful use of the 1.25" filters:

 https://www.cloudyni...h-nikon-lenses/

and here is a link to show results using the 1.25" H-a filter... scroll down 6 images to the Pelican Nebula and click on it.  There are 7 images (to Gamma Cygni) that were all taken with the adapters I cobbled together for the Nikon 300: https://www.cloudyni...-phonetography/

 

I agree that a small telescope is a little easier to use, but results using the fast camera lenses show how good they do perform with NV.  The Nikon does not have a focus lock, but it does have a focusing detent that can be set anywhere within the focus range.  Once focus is found, the detent can be locked down.  The focuser can be moved but returned to exactly the same spot for perfect, repeatable focusing.  The Cannon, Tamron and Sigma 300mm lenses were all fashioned after the Nikon, which was first to use ED lenses.  All 4 of these lenses are held in high regard, even without auto focusing.  And they were each designed to fully illuminate a 35mm sensor (film).  So cropping the light cone to fit through the C-mount hole makes these lenses perform at an equivalent of at least 400mm... I haven't figured out the exact crop factor, but it's pretty significant.

[The Ardent]

In 2015 I started with a couple of cheap old Canon manual focus lenses for handheld NV. Somehow I ended up with a bunch of vintage lenses. It turns out I have a fascination with the old lenses.  After doing some research it seemed that the perfect lens was funnel shaped. Large aperture and fast. In other words, the same type of lens imagers want. Like the Hyperstar, Boren-Simon, Tak Epsilon, and the various "imaging newts" sold today. 

 
It can't be a coincidence that Nikon, Canon, Tamron, Pentax, and Minolta etc all offered a 300 2.8 lens. I can't see them all independently fabricating the exact same lens elements. I wonder if the lens elements all come from the same place, or, is the design is licensed to the different brands? Doesn't matter. What matters for NV , Is there a c-mount adapter available for this lens? The answer to this question limits our choices to the most common consumer brands. 

 
Here's the trap the  lensmakers sprang on us: every brand has a different size drop-in  filter.
Canon 48mm 
Canon recent 52mm
Tamron 43mm 
Nikon 39mm
Minolta 42mm 
Pentax 49mm 
 
These are just examples I found. It's really frustrating - they all offered the same size lens, but no consistent filter size. This is the same game of the C-mount lenses. They all have different size filter threads. 

 

When searching the used telephotos, there are the 400 , 500, and 600mm's. A 600mm f/4 is a six inch diameter lens. I excluded these as not useful for handled use. These focal lengths are the realm of the ubiquitous inexpensive imaging newt, IMO . 

 

Im also interested in the Leica 280mm f/2.8. 

 

Im really excited by the Canon and the results from the other night. 

[chemisted]

I think I have mentioned before that I use a Nikon 200 mm f/2.0 for simply amazing views. Jdbastro's images through a similar lens tells the story.  I picked this up many years ago when digital was all the rage and these were lying around in shops for sale at a reasonable price.  I have done recent searches and it appears these are very hard to come by these days at anywhere close to a good price.  If you happen on one that you can afford snap it up as the 5^o FOV and additional stop are astounding.

[Jeff Morgan]

For my smaller lenses I epoxied in a filter thread ring inside of the C-mount adapter. Not convenient for filter changes, but economical and works well.

 

 

[GeezerGazer]

For my smaller lenses I epoxied in a filter thread ring inside of the C-mount adapter. Not convenient for filter changes, but economical and works well.

 

Jeff, this does work, even with the large 300mm lenses, but the trick is finding a very short filter cell to epoxy into the adapter and using a filter with a similarly short (light path) filter cell.  If either cell is too long, it causes mechanical vignetting.  

 

I was going to epoxy such a cell into my adapter but found that my three H-a filters all caused mild vignetting.  Experimenting, I found the other way to attach filters using the ScopeStuff filter capture ring inside the C2TT adapter.  This method puts the filter very close to the C-mount which eliminates vignetting without modifying anything.  

 

I took an old filter cell and turned it down on my lathe until its total length was only 4mm, but decided on the other method of filter retention.  If anyone needs this short cell to epoxy into a lens adapter, just PM me.  It's free to anyone who can use it.  

 

 

Ray, it seems reasonable that different size filters with different spacings on the lens was used to avoid patent infringement violations... each maker having their own proprietary design parameters.  On each make of lens, the built in filter cells were special so that users would be forced to buy the filters for that specific holder/lens.  Just part of business as usual.  No different than each manufacturer having their own bayonet mount for lenses.  At least there are after market adapters available that allow a Nikon lens to be used on a Cannon camera and vice versa.  

 

You are right about longer telephoto lenses being in the domain of a smaller, less expensive Newt or even a small refractor.  But both options will likely entail mounting a bigger scope if matching the aperture of the equivalent camera lens.  These f:2.8 300mm lenses are very compact, and although heavy at 6+ lbs., are lighter than either a Newt or Frac with equivalent aperture... and, of course, they are faster.  The selection of either option is good, depending on your preferences and needs.  

 

I have a 6" f:4 Newt that is very good visually and takes nice images.  But to get it to f:2.8, requires a reducer/corrector, available from Telescope Service in Germany for $700+ (same as used in the Boren-Simon Newts).  So any monetary savings in the scope is certainly lost to supplemental optics making it as fast as the camera lens but in a bigger package.  There are trade-offs.  

https://www.teleskop...hotography.html

 

If using the lens strictly for visual, then I would certainly buy the Newt or small refractor for their observing convenience.  They are just more comfortable to use when looking up, because the camera lens cannot be adapted for use with a diagonal.

[Jeff Morgan]

Jeff, this does work, even with the large 300mm lenses, but the trick is finding a very short filter cell to epoxy into the adapter and using a filter with a similarly short (light path) filter cell.  If either cell is too long, it causes mechanical vignetting. 

 

I don't have a lathe, so used the RAF ENVIS-> 1.25" astro filter ring. It's .136" tall. The astro filter thread is cut down the entire inside surface.

 

https://www.rafcamer...s-to-astro-1-25

 

Pretty handy rings to have around, think I'll order 5 more this week. 

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[The Ardent]

Here are some single handheld iPhone images taken this weekend. Cropped a little. This is to give you an idea of the view.

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[The Ardent]

Here is a new gallery of pics taken this morning. This is my second attempt at NV iPhone pics with Nightcap. It was a clear morning with the glorious summer Milky Way. Set up the 300mm lens on a tripod, no tracking. Pics were cropped only, no processing. 

 

Looks like i didn't have the phone centered carefully over the NV eyepiece. The bottom left edge is messed up on all the pics. 

 

These pics are intended to represent the actual view. 

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[Vondragonnoggin]

Nice. I just had my Tamron 300mm F/2.8 out the other night for some quick peeks with my pvs-7 in it. My Tamron has been modified with a 2” visual back. The pvs-7 needs a 2” nosepiece + extension tube on it to come to infinity Focus with a 2” Ha filter threaded on the nosepiece. Without the extension the short ScopeStuff nosepiece (could use a 1.25” filter inset in the nosepiece too) just has enough to be gripped by the compression ring but it’s safer with an extension screwed on the nosepiece to make the nosepiece longer.

 

I also have a Tokina 300mm F/2.8 but it doesn’t have the mod done on it and I believe the filter insert is 37.5mm. I could use that one with an F mount adapter that has been modded to fit a 1.25” filter holder in it I suppose, but the Tokina really gets used for daytime regular photography more.

 

They are fun lenses. I have dslr relay lenses for my Litton M942 Monocular that fits mx10160 tubes and NiTec 25mm housing that fits mx9644 gen 2 or mx11620 gen 3 25mm tubes (same as pvs-4)

 

The Tamron with pvs-7:

 

 

The Tokina and NiTec housing with biocular:

 

P

Edited by Vondragonnoggin, 08 May 2019 - 09:58 AM.

[The Ardent]

Today was the hottest day of the year- over 100 deg F. Given the heat and the short window before moonrise, I thought it a good time for NV.

Made some changes to my picture taking:
Canon lens set up on an EQ mount this time.
Nightcap app on the phone instead of the standard phone camera app.
Phone to eyepiece holder, no more handheld.

Each pic is about 10 seconds.

M8 and M20. First unfiltered, second Baader 35nm H-Alpha. Cropped.

Spent some time viewing the Sagittarius and Scutum Milky Way.

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