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The Best Telephoto Lenses for Astrophotography


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The Best Telephoto Lenses for Astrophotography

Rudy E. Kokich

Over the last ten to fifteen years excellent apochromatic telescopes have become available for visual use and photography. Along with improvements in telescope mounts, camera technology, filters, and digital image processing, these have allowed amateurs to produce astrophotographs of nearly professional quality.

However, these APOs have a couple of drawbacks. One is the price, which starts around $800 for the smallest units, and rapidly climbs into thousands of dollars for larger apertures. Another drawback is the focal length. Most of these APOs have F ratios around 6.5, and are unable to comprehend in their field of view large celestial objects such as the Andromeda galaxy, the North America nebula, and comets. Some APOs can be fitted with pricey telecompressors, but those invariably result in vignetting and coma.

Especially for beginning astrophotographers, who should first invest most of their finances into a good telescope mount, telephoto lenses are an excellent and affordable solution. 135mm and 200mm lenses are suitable for wide angle star-field views, and comet and asteroid hunting, while 300mm lenses serve very well for the Andromeda galaxy, large emission nebulae, open clusters, and even larger globular clusters. Aside from being much more affordable, telephoto lenses are easier to transport, easier to mount and easier to guide, and are much more likely to produce encouraging results to a beginner.

Over the years, I have tried more than two dozen telephoto lenses, until I finally found three or four perfect solutions. But first, there are several general rules which must be understood.

Zoom lenses are entirely unsuitable for astrophotography due to prominent aberrations of every kind. They are by nature designed to compromise by magnification and distance, and are therefore not optically optimized at any single setting.

Because of chromatic aberration, no telephoto lens can be used at full aperture. The best ones listed below serve well with a one stop reduction, and some require two or even three stops.

Reducing aperture with the built-in aperture iris interferes with the light path, and results in eight diffraction spikes around bright star images. Some people like these, and consider them decorative. I do not presume to further decorate the universe, and perceive them for what they are: interference. I therefore reduce the aperture at the front end of the lens (as an aperture stop) by screwing in a series of step-down rings into the filter thread. These are affordably available on eBay, and result in perfectly round star images, the way nature intended them to be.

There is some controversy about the use of UV filters, but I found that a good UV filter significantly improves contrast, sharpens small star images, and reduces chromatic aberration. By far the best one is the Tiffen Haze 2 filter. Unfortunately it is not manufactured in a multicoated version, and produces prominent internal reflection artifacts on very bright stars. Nevertheless, it performs excellently on most star fields, and is too cheap not to acquire. The second best, is the Hoya Pro One Digital MC UV(0) filter. I use it routinely in preference to many other multicoated filters I tested, including the new Hoya MC UV©.

All lenses mentioned below are adaptable to Canon EOS cameras with slim EOS adapters which allow the lenses to focus just slightly past infinity. Focusing should be done on moderately bright stars using the 10x magnified Live View. Because of some residual chromatic aberration even with the aperture stop, the best focus lies not where the star image is the smallest, but rather just slightly away from infinity, at the point where the star image barely begins to enlarge. This way the focus will favor the red light which is more objectionable within a star image than a bit of blue.

No telephoto lens can be used with cameras modified by the removal of the internal UV/IR cut filter and anti-aliasing filter. Such "full spectrum" cameras are somewhat more sensitive in the ultraviolet, but much more sensitive in the deep red and infrared. No telephoto lens, and no apochromat, is sufficiently corrected to accomodate such a wide spectral range. Whereas quality apochromats can be corrected with broad band filters, such as the Astronomik UV/IR cut filter or the CLS-CCD filter, telephoto lenses can not. However, they can be perfectly corrected with narrow band H-alpha or OIII filters.

Finally, to prevent image shift during exposure, all telephoto lenses must be supported at two points: at the camera end, and at the far end with a large retaining ring. To prevent damage to the lens finish, apply nylon acorn nuts (or cap nuts) to the tips of the retaining ring's three alignment screws. The screws should be set sufficiently tightly to prevent shift, yet not so tightly as to interfere with fine focusing.

It may be superfluous to add, but it can't do any harm, that in astrophotography all shutter control must be done with a wired or wireless electrical shutter release swith. Touching the telescope, even ever so slightly, will introduce vibrations which will ruin the photograph. Also, accurate guiding is essential. If the telescope mount is precisely aligned to the celestial north pole, unguided exposures of one to two minutes are possible. A series of such images can be digitally stacked to produce excellent results. However, I find the process tedious, and prefer single, manually guided, long exposures which seem to have deeper colors. My guidescope is a 5in F5 Jaeger's achromat with a 2.3x Barlow, and a 9mm illuminated reticle eyepiece. This gives me the power of 162x, which is barely sufficient for my 420mm fl APO astrograph at full camera resolution. Extrapolating from this, minimum recommended guidescope power is 120x for the 300mm telephoto, 80x for the 200mm, and 55x for the 135mm.

The first telephoto lens of choice, especially recommended for beginners, is the 135mm F2.5 SMC Pentax. This lens has the Pentax K bayonet mount, and requires the K-EOS adapter for attachment to Canon EOS cameras. When the aperture is stopped down to 37mm using step-down filter rings, this lens produces incredibly tiny pinpoint star images from edge to edge. In this configuration, the lens is still a very fast F3.4. The lens is available on eBay for around $200. It must not be confused with the much cheaper SMC Takumar, often deceptively advertised as SMC Pentax Takumar, which has the M42 camera thread, and is plagued with unextinguishable blue chromatic aberration.

The best 200mm lens is precisely the older 200mm F4 SMC Takumar, which comes with the M42 camera thread, and requires the M42-EOS adapter. When stopped down to 37mm, at F5.4, it also produces perfect, small and round star images across the entire field. It has just a hint of chromatic aberration on very bright stars and, if highly enlarged by 400-800%, the stars in the very corners barely begin to show a touch of astigmatism. These lenses can be had on eBay in mint condition for around $70, and are probably the most price efficient optical instrument in the world. Take care not to confuse this lens with the 200mm F4 SMC Takumar 6x7 which has a different optical configuration, and which I have never tested. Also, the newer and much more expensive 200mm F4 SMC Pentax with the K mount is decisively inferior, showing small but annoying red chromatic aberration.

The next 200mm lens of excellent quality is the 200mm F4 Nikkor F which requires the Nikon F to EOS adapter. When stopped down to 37mm, F5.4, it is almost identical to the Takumar except that on highly enlarged images it shows a hint of coma in the distant corners. In excellent condition, this lens retails for around $200. Selecting between it and the 200mm Takumar was not an easy choice but, in the end, I chose the Takumar because it seemed to have slightly better contrast.

The one and only 300mm lens I tested is the Zeiss Tele-Tessar 300mm F4. There was no reason to test any other because, when stopped down to 49mm, F6.1, this lens is simply perfect, comparable to any APO on the market. It has no chromatic aberration, and no hint of star deformities in the corners. It requires the Contax-EOS adapter for attachment to the camera. I bought my lens in mint condition for $350 from Japan, but I see that some retailers are asking significantly more. This lens has only two drawbacks. One is its size and weight, which requires a sturdy support on the telescope. The other one is the inevitable and persistent regret that, because of chromatic aberration, the full 75mm aperture of this beautiful lens can not be used in full visible spectrum photography. However, I am convinced that its large aperture and fast F ratio would perform exceptionally well in three color or narrow band H-alpha and OIII photography.

M13, Hercules, Zeiss 49-300mm, exp 163 seconds, iso 800, Hoya MC UV(0) filter. Note the small galaxy NGC 6207 in
the 2 o'clock position from the great cluster. (Click the image to load full-sized version.)


  • ChipAtNight, Fox1971, macaddict and 6 others like this


85 Comments

No one yet mentioned a zoom lens, I had an opportunity to test my Canon 24-105L f/4 on M31 Andromeda Galaxy and received wonderful results with Canon 60D unmoded, I set it to 105mm, No vignatting, slight coma on the corners and no false color on bright stars.
Looking forward to allow purchasing the Canon 200mm f/2.8L II USM.

 

Cheers,
Lior

My experience with zooms has been elimination of focus creep, it can really mess up a night of imaging if it happens. On a lens like yours it may be less of an issue, mine was a cheaper low end sigma lens, like $125

Ron,

You have a good point. I am sorry if the article following the title disappointed you.

I agree the more appropriate title would be "The Best Old Telephoto Lenses I Have Tested for Astrophotography", but I don't know how to make the change. If the moderator is following, he can feel free to do so.

On the other hand, other members are contributing very useful information about NEW lenses, so the original title acquires a bit more meaning as these comments are included.

My intention was certainly not to EXCLUDE any lenses, or to imply that the old lenses are better than the new fluorite lenses like the Canon EF 600mm f/4L IS II USM.

Regards,

Rudy

Photo
Michael Covington
Jun 30 2015 10:57 PM

Thanks to all for starting this discussion!

I looked up the Zeiss 300/4 Tele-Tessar for Contax/Yashica.  Its MTF curves are impressive (all the more because from Zeiss they are measured, not calculated).  That lens is indeed a very good deal for the money (and fits Canon DSLRs with an adapter).

Someone mentioned zooms.  I have gotten moderately good results from zooms at their maximum focal length.  A zoom is compromise, but some of the best modern zooms are quite good.

My Olympus 300/4.5, back in the day, disappointed me; the Nikon 300/4 was sharper and the Canon 300/4 was sharper yet.

Clear skies, all!

Dave Venne,

I started astroimaging decades ago using the Spiratone 135mm F1.8 lens at full aperture. It had horrendous chromatic aberration which completely disappeared when I applied a Red 25A filter, he he. Coma also became acceptable when I reduced the aperture by one stop. I have many black and white negatives on TriX film of extensive emission nebulosities which look beautiful even by today's standards.

I think most "decent" old lenses would be quite suitable for narrow band and RGB photography, so long as you refocus each color.

Rudy

    • Michael Covington likes this

MCovington,
The Zeiss Tele Tessar 300/4 really is a great lens. Here is an image of the Ring Nebula I took with it using an unmodified T3i, iso 400, manually guided 6 min exposure, no filters, right edge 20% crop. Aperture was reduced to 49mm with filter thread step down rings. The nebula is only 2' 30" in size, yet still looks cute. I think a beginner would be quite happy with a wide range of celestial objects using this lens.
see link

http://www.cloudynig...le-tessar-3004/

Rudy

 

    • Michael Covington likes this

I have a 200mm 1.8 USM I have want to try out

Ron,

You have a good point. I am sorry if the article following the title disappointed you.

I agree the more appropriate title would be "The Best Old Telephoto Lenses I Have Tested for Astrophotography", but I don't know how to make the change. If the moderator is following, he can feel free to do so.

On the other hand, other members are contributing very useful information about NEW lenses, so the original title acquires a bit more meaning as these comments are included.

My intention was certainly not to EXCLUDE any lenses, or to imply that the old lenses are better than the new fluorite lenses like the Canon EF 600mm f/4L IS II USM.

Regards,

Rudy

 

I've changed the title of this topic in accordance with your above quoted post.

 

Bob (mayidunk, Co-Moderator, Discussion of CN Articles, Reviews, and Reports)

Hello All,

I do astrophotography with telephoto lenses since some years and would like to add my two cents on the thread mentioning the Nikon Nikkor Ai 300mm ED f4.5 non internal focus telephoto lens.

 

This lens is rare to find (I looked for it quite some time after reading Bjorn Roslett opinions) as Nikon moved after one year of production to the newer design with internal focus.

Quite sharp, it lacks the red-dot for IR focus because visual and IR focus coincide.

I can confirm it is a true apochromat and with very flat filed on APS-C DSLR.

 

The stars may not be as tight on high class refractors of similar size (71mm front lens diameter) but nice anyways and, due to my limited time for the hobby, I found valuable the speed yeld by f/4.5 aperture (when refractors are typically f/6-f/7).

 

Also, the Nikon Nikkor Ai-S 180 f/2.8 ED (I own one as well) and LEICA Apo-Telyt 180 f/3.5 are both highly regarded lenses for astrophotography, the latter being probably the best of all although pricey.

 

Kind Regards,

Marco

    • gene williams likes this

I can put in a great word for the nikkor AF-S 300mm f/4. Wide open its a piece of work minimal to no aberrations, coma well controlled and very sharp all over, just like my 14-24mm is at 24mm... Edge to edge corner to corner.

 

Huzzah

Photo
BarrySimon615
Jul 03 2015 09:20 AM

Shortly after I got my Canon 20D back in 2004 I bought a special adapter (cost me better than $150.00) that allowed me to adapt all of my Olympus Zuiko lens to the EOS mount lens.

Like an earlier post, I too was disappointed earlier with my Olympus Zuiko 300 f/4.5 for similar reasons, but the very moderately priced Zuiko 200 f/4 was always a great lens as is the Zuiko 135 f/2.8.  The 200 f/4 is a lens that I use with the Canon 20D and a more recently acquired 60D.  Always wide open.

While many earlier lens are now available at nice prices, there are a few that have crazy high prices.  One other Zuiko lens that is superb but crazy high expensive is the 100 f/2.  It has ED/SD glass and a very flat field.  The one drawback for me with this lens was that the focus ring was very sensitive.  Money talks and I kept the 135 f/2.8 which KEH would have only paid me about $50.00 for.  (They gave me $500.00 for the 100 f/2.)

Another good one is the Tamron 90 mm f/2.5.

 

See photos with the Olympus Zuiko 200 f/4 here. (4th post in the thread.)

http://www.cloudynig...le-tessar-3004/

 

The first photo in my post is a 2 minute exposure with the 200 f/4 wide open at ISO 400, a single exposure.  The second photo is a copy of the same one but brightness, contrast and color tweaked.  The shots have not been cropped in any way.


Barry Simon

Barry,

You could entirely eliminate those red rings around the stars by making the following changes:

-Keep the lens iris wide open to avoid diffraction spikes, but reduce front aperture with filter step-down rings from 50 to 37mm

-Use a Hoya Digital MC UV(0) filter. Tiffen Haze 2 is much better, but is uncoated, and not suitable for very bright stars

-Focus the camera with 10x magnified live view NOT at what seems like the smallest star image but very slightly AWAY from infinity. The lens would be moving ever so slightly away from the camera. This brings residual red CA into perfect focus. UV and violet will be slightly defocused, but will be blocked by the UV filter.

Give it a try. You will not believe the improvement.

An alternative, when photographing emission nebulae, would be to use a multicoated deep red filter. In that case you could probably use full aperture, no UV filter, and focus to the smallest star image.

If you use full sensor resolution, careful guiding, and iso =<400, such images still look good when cropped 25%.

Please send in your new images.

Regards,

Rudy

Photo
BarrySimon615
Jul 04 2015 09:18 AM

Thanks Rudy!  I have also used a Lumicon Deep Sky filter in some shots.  It really brings out nebulosity.  When you say very slightly AWAY from infinity does that mean before the Infinity mark on the focus ring or slightly beyond the mark.

 

In the next week I will be going to the Davis Mountains in west Texas for some observing and photography.  My friends and I will be staying at Casa Mano Prieto which is about half way between Ft. Davis and Marfa.  The owner is an amateur astronomer and he has a 12.5 inch RC on a Paramount under a dome.  We may do some observing there but as one of my friends worked on several of the observatory building projects at McDonald we have secured permission to set up our own scopes on one of the foundation pads that does not yet have an observatory.  How spectacular is that!  

 

I will be shooting some shots using my Explore Scientific 80mm f/6 triplet with a TeleVue reducer/corrector so the amended focal length will be 384 mm and f/4.8.  I will also shoot some shots with the Zuiko 200 f/4 and I will perhaps try a few more with my Zuiko 24 at both f/2.8 and a bit slower.  Maybe also my Tamron 10-24 mm at the 10 mm setting.  Time permitting I will take a few test shots from the backyard this coming week to see if this is worthwhile.

 

The ES 80 will be piggybacked on either my Orion ST120 or my SkyWatcher 100ED, not sure yet which one I will bring.  All of this will ride on my Celestron AVX mount. I think I am favoring the ST120 for it's light gathering and wide field of view.  I think photography thru this scope will be pretty worthless due to the fact that it is a fast achromat, but maybe with the Lumicon Deep Sky it will be ok.  (Photos thru my Jaegers 6" f/5 are nice with the Deep Sky Filter.)  Other equipment that will be brought by my minions include a TEC 140 riding on an AP 900 mount. Keeping my fingers and toes crossed for clear skies!

 

Barry Simon

Barry,

 

When I say AWAY from infinity I mean the following:

-Turn the focusing ring all the way toward infinity till the barrel stops. The lens will be moving closer to the camera.

-Now focus AWAY from infinity, the only direction possible. The lens will be moving away from the camera.

-In 10x magnified live view you will see a point where the star image appears to be the smallest. You are now focused on green, where the sensor has the highest sensitivity. On bright stars only you might notice slight red haze around the tiny star image. This is the red which is not in perfect focus

-Focus further away from infinity ever so slightly till the star image just barely begins to increase in size. You are now focusing red, and slightly defocusing the blue.

Keep in mind that focusing ring movements are very, very minute.

I usually take a few test shots in the process and look at magnified star images to make sure that the red rings are gone.

This process is not necessary with mirror and true APO optics, where you would focus to the very smallest star image.

 

OK on your Jaegers 6" F5. As a kid in mid 70's, I spent many hours hanging around the Jaegers' store/factory in Lynbrook, and got to know the staff and the old man himself. He sold me a "hand-picked" 5" F5 and a 3" F5, both of which have very little color and resolve very close to the Dawes limit. They remained my favorite, convenient telescopes over the decades, along with an exceptionally good C5 for lunar, planetary and spectroscopy work. Since I bought an APO a couple of years ago, I am also using the Jaegers 5" as an excellent guidescope, while the 3" Jaegers works as a guidescope for telephoto lenses up to 200mm.

 

Well, it looks like you are heading out for a great astrophotography adventure. I wish you clear, dark and steady skies, and hope you will share some good images with us when you return.

 

Rudy

 

 

Photo
Michael Covington
Jul 04 2015 08:29 PM

MCovington,
The Zeiss Tele Tessar 300/4 really is a great lens. Here is an image of the Ring Nebula I took with it using an unmodified T3i, iso 400, manually guided 6 min exposure, no filters, right edge 20% crop. Aperture was reduced to 49mm with filter thread step down rings. The nebula is only 2' 30" in size, yet still looks cute. I think a beginner would be quite happy with a wide range of celestial objects using this lens.
see link

http://www.cloudynig...le-tessar-3004/

Rudy

That is as good as my Canon, at half to a third the price.

The lenses I've used for wide field work that have worked really well are:

 

nikon 300mm f/2.8 vr 2.  It's heavy, so bring a good tripod.  But the glass is phenomenal.

 

Nikon 16mm f/2.8.  Very little distortion that is easily corrected in Photoshop.  You need to stop in down to avoid the 'seagulls' in the corner.  f/4 works OK.  You can just about get the entire milky way on a full frame chip.

 

Nikon 50mm f/1.4.  Amazing lens.  Pretty flat field. 'nuff said.

 

Nikon 70-200mm f/2.8 vr.  Great images for a zoom.  My understanding is the 'non-vr' lens produces even sharper images.  I'm going to try it in a few months.

 

Enjoy!

 

Chris

Photo
Falconstare
Jul 15 2015 08:29 PM

Thank you for sharing, I learned a lot as a beginner in this field and would recommend to my friends.

Photo
Michael Miles
Jul 16 2015 04:46 PM
Thanks Rudy:

I've been looking for a decent lens in the 200mm range, so I've ordered a Takumar thanks to you. It's coming from Japan and should get here next week (so should rain next week - the farmers can thank me ). Michael

A couple things I'd like to add from my own experience:

 

1.) If you are going to get any kind of filter for your lenses make sure it is not a clip-in filter. Almost all the new lens will not fit on the camera with this type of filter. Go with a filter that attaches to the front of the lens. The clip-in filters work great for when you are attaching the camera to an actual telescope. 

 

2.) I do not agree specifically with your statements on the specific amount of mag needed to guide at certain FL of the lens. I image with a 80mm Equinox frac with a .76x reducer which brings its FL down to 380mm. I use a 50mm finderscope that you get with any telescope and with a little DIY attached a guide cam on the back. No reducers or barlows. I can consistently achieve 15min subs on my Orion Sirius mount. Even without guiding I can get 2min subs with just a decent PA. Now I know that the mount has a lot to play into how accurate the tracking is but with the much shorter FL and much less overall weight of a DSRL+lens (compared to a telescope) you dont need much to guide with and really achieve some long subs. I will agree with you that the longer your subs are the better your end result will be and you will need less total data as well. 

3.) I think you are really throwing a lot of mud on APO refractors when it isnt needed and you have some of your facts wrong. So there are several point I'll hit up here. Firstly, there are some very nice doublet APOs out there that have a starting price well below $800 and thats new. AT and WO both have small frac (60-80mm) that are in the $400-600 range. Yes the better doublets are closer to $800 or over but there are plenty of other options out there as well. Then on top of that you hit up the used section and you can find them for an addition 30-50% off new price. Secondly, suggesting that fracs can't fit any of the larger DSOs is a bit of a stretch. Your imaging FoV isnt just about FL, its also about your camera chip size. Since this topic is talking about DSLRs for the most part I will not jump over to CCDs. But DSLRs tend to have a very large chip in them which really helps with imaging the large DSOs, though different DSLRs do have different sizes so not all are the same. With my Canon 450D at 380mm I easily fit M31 and M42+M43 all on my chip with plenty of room around them. And those are two of the larger DSOs up there and there are fracs with even shorter FL than what I was imaging.  at. Lastly I don't know what telecompressor you where using with your APOs but the ones out today don't cause vignetting or coma. That is if you get the proper ones for imaging and for your specific scope. Most reducers today are also a field flattener so neither vignetting or coma should happen. 

I do want to make it clear that I am not against imaging with lenses at all. For ultra wide FoV(I consider that anything under 300mm FL)lenses are the only way to go. I also agree they are great starters as they are much cheaper and need less equipment in the end. Thats what I started with. I just think you where bashing fracs a bit much in the beginning and made it sound like they arent really for beginners and that all beginners should start with lenses. Now I dont know if thats what you meant or not but that how i took it. APO frac are great for beginners if people really what to get into imaging. Again nothing wrong with starting with lenses either. There's more than 1 way to get into imaging and the only right way is the way that makes that person happy. 

Photo
Michael Covington
Jul 16 2015 10:10 PM

A couple things I'd like to add from my own experience:

 

1.) If you are going to get any kind of filter for your lenses make sure it is not a clip-in filter. Almost all the new lens will not fit on the camera with this type of filter. Go with a filter that attaches to the front of the lens. The clip-in filters work great for when you are attaching the camera to an actual telescope. 

 

 

To be precise, clip-in filters for Canons fit in the space that is occupied by an EF-S lens but not an EF lens, as I understand it, and so cannot be used with an EF-S lens.  Canon makes two series of lenses, EF and EF-S.  The latter are only for smaller (APS-C) DSLRs.  The former are their regular lenses.

    • gene williams likes this

nmoushon,

 

1) You are correct that most NEW lenses do not fit the camera when clip-in filters are installed. That was the case with my Canon kit lens. However, OLD telephoto lenses with T-EOS, Pentax K-EOS, Pentax M42-EOS, and Contax-EOS adapters do fit very well. I routinely use the Astronomik CLS-CCD clip filter with all of these. I think Pentax 6x7-EOS adapters would also work well.

 

2) You are again correct that guidescope magnification does not need to be very high when using auto-guiders with a guide camera. Such devices are sensitive to shifts in guide star position of 1 pixel and, according to Orion, a 50mm autoguider serves well for fl up to 1500mm. Also, if the mount is well calibrated and centered to the pole, it is quite possible to get decent 1-2 min subs at fl around 400mm without guiding at all. Furthermore, required guidescope magnification also depends on the selected image resolution and the expected image quality.

 

Personally I use maximum image resolution (5184 pixels horizontal), and expect the smallest star images to fall within a 6 pixel circle. I do exclusively manually guided long exposures. With my Canon 600D camera (APS-C sensor size 22.2mm horizontally) and a small TSAPO65Q astrograph with 420mm focal length, the calculations go as follows:

 

Pixel Size = 22.2mm / 5184 = 0.00428mm = 4.28 microns
Arcsec/Pixel = 3600 x ATAN (0.00428 / 420)) = 2.10 arcsec/pixel = 12.6 arcsec / 6 pixels

 

Therefore, I have to guide 10-12 minute exposures to an accuracy of less than 10 arcsec. For that purpose I use a 5in f5 guidescope, 2.3x Barlow, and a 9mm illuminated reticle eyepiece. This gives me the magnification of 162 X, which is barely sufficient. For maximum resolution manually guided long exposure photography I would recommend the following formula:

 

Minimum Guidescope Magnification = Lens FL / 2.6

 

Such images are very crisp, and can be cropped 20-25% while still yielding excellent results

 

3) I do not recall throwing mud on ANY telescopes. I am merely pointing out that some of the old telephoto lenses I have tried, when used correctly (usually with 30-35% aperture reduction) produce truly outstanding images which would satisfy even advanced amateurs. They are certainly excellent, low cost optical systems for beginning astrophotographers.

 

http://www.cloudynig...le-tessar-3004/
http://www.cloudynig...e-tessar-300-4/

 

Your next point is sensor size. I have two Canon 600D cameras, modified and unmodified, which have the APS-C sensor. Large objects, such as the Andromeda galaxy, or N America nebula do not entirely fit into the frame of my astrograph. Rather than byuing a full frame camera, I chose a much cheaper alternative: a Zeiss 300/4 telephoto lens.

 

I received several image samples from Teleskop Service taken with their astrographs and a 0.8x telecompressor. ALL showed distinct vignetting and a bit of coma in the corners. So, again, I chose a shorter focal length telephoto in preference to a pretty costly telecompressor.

 

Finally, I wish to assure you that I do not mean to discourage beginners from any particular telescope. They can start with the Keck Observatory telescopes as far as I am concerned. I simply think that an affordable 135mm or a 200mm telephoto on top of a decent guidescope is a good way to start learning and producing satisfying results.

 

Regards,
Rudy

Finally! first light for my Canon 200mm F2.8L USM II 

For some reason I cannot upload an image to this post so here is  a link.

 

https://www.flickr.c...04/19220641704/

 

9 subs taken in haste as I had a mount issue and then clouds were closing in just as I started.

This was wide open at F2.8 so I have ordered step down rings in lieu of using the internal leaves which will cause spikes (I smile to hear photographers talking about a lens' "bokeh" like it's something desirable). Sensor temps were 133F for the first images then cooled down a little after that so you can imagine the noise. I decided I like using camera kit in the field and am thinking of a 1.4 teleconverter as I read that this lens takes one very well.

    • gene williams likes this

Kevin,

What a wonderful lens! You will spend many thrilling nights with her to the detriment of your other relationships.

Pinpoints from corner to corner at full aperture. There is just a bit of chromatic aberration which will probably clear with only a 1/2 stop reduction.

Also, try adding the Hoya Pro-1 Digital MC UV (0) filter, not the new UV©.

Please send information regarding location, mount, exposure times, ISO, and the stacking program you used.

Regards,

Rudy

 

I tried using an Astronomic CLS but then ran into mount problems and removed it to simplify things as clouds were forming up. The CLS changes focal length and is also very dark for composing. 

 

Charlie Elliot Wildlife Refuge near Mansfield Ga.

Canon T4i (stock) w 200mm F2.8L USM II

9X180s @ISO400, 30 Darks, 30 flats, Master bias

Celestron AVX, Starshoot Autoguider w50mm,

BYEOS

PixInsight

Thanks for the info, Kevin. I am looking forward to more photos with this lens.

On another subject, I see you have a couple of homebuilt 5 inch achromats. I also have 3" f5 and 5" f5 Jaeger's achromats I use as guidescopes. I buit them decades ago when Jaeger's was still in business. Where did you get the hardware to put together those telescopes: 5" lens cells, aluminum tubes, and focusing mounts which all fit together?

Regards,

Rudy

Rudy, 

 

I think this thread will answer your questions...

 

http://www.cloudynig...actor-assembly/

 

I cannot find the build thread on the F5.5 scope but it's construction was similar.

Except the focuser is modified from a Newtonian type and there's no secondary draw tube. 

 

The F9.4 gives great (but dark) views and I love to put binoviewers in it to look at the Sun and Moon. 

Bright nebula actually look good too!

https://flic.kr/p/uwjuJD



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