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mirror lens for Mercury transit

astrophotography dslr imaging solar catadioptric
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#1 Nicole Sharp

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Posted 06 August 2019 - 03:22 AM

What does anyone think about using a 500/79 (500-mm f/6.3) catadioptric mirror lens on a Canon APS-C camera to record the November 2019 Mercury transit with?

 

79 mm (minus the central obstruction) should be enough aperture to show Mercury as a disc, and the sampling would be decent at 500/79 with a resolution of 6000*4000, and also at 1000/79 with a 2X extender and a lowered resolution of (e.g.) 1920*1080.

 

Great idea for recording the Mercury transit on a budget without a telescope?  Or would be terrible results compared to say an AT60ED (360/60 semiapo refractor)?

 

https://www.amazon.com/dp/B014JS9DEW/

 

Would need a Solar filter of course, and a means to Solar-align the APS-C DSLR camera at 500 mm or 1000 mm.


Edited by Nicole Sharp, 06 August 2019 - 04:09 AM.


#2 Nicole Sharp

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Posted 06 August 2019 - 03:50 AM

Found this:

 

https://www.fourmila...-05/001609.html

 

Seems pretty decent for imaging on a budget?  Not sure how the Nikon 500-mm f/8 (500/63) compares to the Bower 500-mm f/6.3 (500/79) in optical quality, but the increased aperture should increase the resolution even better.

 

How well would that work for stacking frames from short video clips at 1080p60 at 2*500/79?


Edited by Nicole Sharp, 06 August 2019 - 03:58 AM.


#3 Nicole Sharp

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Posted 06 August 2019 - 04:06 AM

Found another photo at f/16 (2*500/63):

 

http://www.theastron...07_0725_wgw.jpg

 

That looks really nice.  So what I am thinking is to just get a DSLR body and then the Bower 500-mm f/6.3 mirror lens (2*500/79) if I can't get the DSLR working in the Newtonian at 2*500/114 or 1000/114.

 

Let me know if you have anything terrible to say about the Bower lens, or if there might be a better alternative.  I like it for its price.


Edited by Nicole Sharp, 06 August 2019 - 04:07 AM.


#4 TOMDEY

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Posted 06 August 2019 - 06:28 AM

Hi, Nicole! Well, it is certainly well within good resolution with your equipment. I believe the planet is well over ten arc-sec across. And the exposures are nice and short... so it's an easy target - event not to be missed! Here's mine from back on May 9th, 2016... using similar apertures. I found that a green filter with the 100mm F/6 APO Refractor helped the resolution a lot.    Tom

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  • 174.1 transit 0832amedt jpg.jpg


#5 TOMDEY

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Posted 06 August 2019 - 06:29 AM

and this one with the Lunt 80mm Ha

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  • 172.2 mercury transit 2 0801amedt jpg.jpg

Edited by TOMDEY, 06 August 2019 - 06:30 AM.


#6 rolo

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Posted 06 August 2019 - 06:37 AM

Off brand mirror lenses are usually not a good choice. The Nikon 500mm f/8 can be excellent though, I  have one and its very sharp.

 

Another concern may be the focal length cause Mercury is very small.

 

Here's a pic of the last transit with a C8 (2000mm f/10) and full frame DSLR

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  • MercC8-72.jpg

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#7 Nicole Sharp

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Posted 06 August 2019 - 07:15 AM

That second photo was supposedly with a Canon 500-mm f/8, but I've never seen a mirror lens in the Canon catalog, so might have been discontinued.  A Nikon lens might get upset if you tried to use it with a Canon camera.  But I want f/6 instead of f/8 if I can get it.

 

The whole point of using a mirror lens though is for low cost and low weight, so trying to get a more expensive name-brand lens would defeat the point a little bit.  I would like to put it on an iOptron CubePro with an 8-pound payload limit (including camera and accessories):

 

https://cdn3.volusio...otos/8200-4.jpg

 

With the CubePro, I could do a side-by-side setup to film simultaneously at 1000/79 with an APS-C DSLR and also at (e.g.) 3000/114 (120X with a 25-mm eyepiece and 3X Barlow) afocally with a smartphone camera, if I can't use the DSLR camera at prime focus on the Newtonian.

 

I haven't seen any consistently negative reviews on the Bower 500-mm f/6.3, and people do seem to be using it at least for Lunar imaging.  I was thinking of putting the Baader ASBF 80 on it since it is only filter-threaded in the rear.

 

https://www.bowerusa...o-t-mount-lens/

 

https://www.highpoin...-filter-asbf80/


Edited by Nicole Sharp, 06 August 2019 - 07:31 AM.


#8 rigel123

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Posted 07 August 2019 - 06:05 AM

Would this be a lens you plan to keep on using for other photos or is it more than likely going to just sit on a shelf gathering dust?  Have you considered something like this that you can use and send back and get a guaranteed good lens for this occasion?  You can rent the most expensive or something like the Tamrons that are great lenses but less than the one you are looking to buy.

 

https://www.borrowle...hString=Tamron


Edited by rigel123, 07 August 2019 - 06:07 AM.


#9 Nicole Sharp

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Posted 07 August 2019 - 07:14 AM

Would this be a lens you plan to keep on using for other photos or is it more than likely going to just sit on a shelf gathering dust?  Have you considered something like this that you can use and send back and get a guaranteed good lens for this occasion?  You can rent the most expensive or something like the Tamrons that are great lenses but less than the one you are looking to buy.

 

https://www.borrowle...hString=Tamron

 

There are some really amazing DSO images on AstroBin.com with mirror lenses on low-cost tracking mounts just by stacking hundreds of 30-second exposures.  Definitely seems like the Maksutov-famous "apo-like" performance for a fraction of the cost and weight.

 

I would actually plan to keep this as my only DSLR lens (if I get the DSLR as body-only), especially if I can't use the DSLR at 500/114 in the Newtonian.  From what I can see so far, it seems like it should be great for Solar and Lunar imaging, as well as some basic planetary imaging (Jupiter, Mercury transit), plus as a lightweight supertelephoto lens for Terrestrial photography as well.  I am really surprised by the DSO images I found, so am pretty excited to try that too.  I think that the low weight really helps on the budget tracking mounts (where every ounce can count toward minimizing payload for the best performance).  A similar (semi)apochromatic refractor would weigh about 4 times as much (and cost about 4 times as much).

 

I may eventually try to get both a 500-mm f/6.3 and also a 300-mm f/6.3.  The 300-mm f/6.3 would be a lot better for short-exposure imaging of M31 on a tracking mount.  Not sure if a focal reducer would work with the 500 mm

 

NASA's "Mr. Eclipse" also recommends mirror lenses for basic imaging of Solar eclipses on a budget, so seems like a pretty good idea.


Edited by Nicole Sharp, 07 August 2019 - 07:30 AM.


#10 rigel123

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Posted 07 August 2019 - 07:20 AM

I missed that you didn't have the DSLR body yet. I have a 500mm mirror lens that I can't even remember how I got but images just weren't very sharp but they may have improved these lenses a lot. At the price it may do exactly what you need for what you want to do. If they have a return policy you could always get it and if it's a dud just turn it back in.

#11 Nicole Sharp

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Posted 07 August 2019 - 07:26 AM

I actually did look into renting a DSLR camera and a Celestron NexStar 6SE from BorrowLenses.com for the Mercury transit though.  It would be surprisingly affordable.  But they do not rent Solar filters!!!  I would have to buy a Solar filter for a rented telescope :-O .  And the rental period would not be long enough for me to really become familiar with the equipment.  Ideally, I would want months of practice and several trial runs before the actual event.


Edited by Nicole Sharp, 07 August 2019 - 07:26 AM.


#12 rigel123

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Posted 07 August 2019 - 07:36 AM

I might start out by getting a Baader Solar Filter for your Meade StarNavigator and see if you can get an image with the camera body directly on the scope or try eyepiece projection. It has a tracking mount (I assume). I got a pic of the Venus Transit years ago simply by holding my DSLR up to an eyepiece on my home made 8" Newtonian. (That was back in the days of film so I really didn't know if I got anything until I had the pictures processed!!

#13 Nicole Sharp

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Posted 07 August 2019 - 07:56 AM

I might start out by getting a Baader Solar Filter for your Meade StarNavigator and see if you can get an image with the camera body directly on the scope or try eyepiece projection. It has a tracking mount (I assume). I got a pic of the Venus Transit years ago simply by holding my DSLR up to an eyepiece on my home made 8" Newtonian. (That was back in the days of film so I really didn't know if I got anything until I had the pictures processed!!

Yes, I am trying to avoid my mistakes from the 2017 Solar eclipse.  This time, I have a threefold imaging plan:

 

Plan A: image the Mercury transit afocally with a smartphone camera at 2*500/114 or 1000/114 (but that didn't work out too well in 2017).

 

Plan B: image the Mercury transit with a prime-focus DSLR camera at 2*500/114 or 1000/114 or 3*500/114 or 2*1000/114

 

Plan C: image the Mercury transit with a 2*500/79 mirror lens on a DSLR camera (if I cannot get the DSLR to work with the Newtonian)

 

So I have several different affordable imaging options available to make sure I don't miss out and nothing goes wrong (other than weather or car trouble I guess).

 

This is the mount I am thinking of getting, which is really perfect for a side-by-side setup at two different fields of view (full-disc and close-up) using two cameras (afocal smartphone camera and DSLR camera):

 

https://cdn3.volusio....jpg?1531900697

 

https://cdn3.volusio....jpg?1531900697


Edited by Nicole Sharp, 07 August 2019 - 07:57 AM.


#14 Nicole Sharp

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Posted 07 August 2019 - 08:06 AM

I might start out by getting a Baader Solar Filter for your Meade StarNavigator and see if you can get an image with the camera body directly on the scope or try eyepiece projection. It has a tracking mount (I assume). I got a pic of the Venus Transit years ago simply by holding my DSLR up to an eyepiece on my home made 8" Newtonian. (That was back in the days of film so I really didn't know if I got anything until I had the pictures processed!!

 

Hmmm.  I did not think of eyepiece projection.  The concern I had was what is likely the extremely small image circle, which is small enough that even with a 3X Barlow may still not be large enough to fully illuminate a 27-mm sensor.  I don't know how that correlates to eyepiece projection though??  What would the sensor illumination be like?  I figure no matter what I try, there is going to be vignetting on the APS-C sensor in the small Newtonian?


Edited by Nicole Sharp, 07 August 2019 - 08:09 AM.


#15 Nicole Sharp

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Posted 07 August 2019 - 08:09 AM

I might start out by getting a Baader Solar Filter for your Meade StarNavigator and see if you can get an image with the camera body directly on the scope or try eyepiece projection. It has a tracking mount (I assume). I got a pic of the Venus Transit years ago simply by holding my DSLR up to an eyepiece on my home made 8" Newtonian. (That was back in the days of film so I really didn't know if I got anything until I had the pictures processed!!

I considered afocal DSLR imaging as well.  What kind of lens did you use?  I figure only a macro lens would be able to get close enough to the eyepiece?



#16 rigel123

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Posted 07 August 2019 - 08:37 AM

Hmmm.  I did not think of eyepiece projection.  The concern I had was what is likely the extremely small image circle, which is small enough that even with a 3X Barlow may still not be large enough to fully illuminate a 27-mm sensor.  I don't know how that correlates to eyepiece projection though??  What would the sensor illumination be like?  I figure no matter what I try, there is going to be vignetting on the APS-C sensor in the small Newtonian?


Someone on here can probably give you the formula for figuring out the eyepiece, etc for getting the image circle at the size you want on the DSLR that you choose. Of course you would need a bracket to hold the camera to the scope/focuser. I'm kind of a slap stuff together and make adjustments kind of guy. I wouldn't recommend doing what I did to get the shot of the transit of Venus where I simply held the camera up to the eyepiece and shot away when it looked right! That was a long time ago and since then I have acquired much better setups for imaging the sun! The nice thing is you have plenty of time to put your system together and practice taking shots of the sun now. And at the time of the transit you have about 6 hours to try and capture a nice shot rather than 2 minutes of panic during an eclipse!

#17 rigel123

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Posted 07 August 2019 - 08:40 AM

I considered afocal DSLR imaging as well.  What kind of lens did you use?  I figure only a macro lens would be able to get close enough to the eyepiece?


If I remember correctly it was a stock 50mm lens on my old Pentax K1000 that I held up to the eyepiece which was probably a 24mm or 12mm Kellner. I got about 1/4 of the disk of the sun doing that.

#18 marktownley

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Posted 07 August 2019 - 11:35 AM

Whatever you go with I would thoroughly practice all these setups on the moon beforehand.
 

I might be wrong but a DSLR on a 114mm newtonian seems rather imbalanced to me - will the focuser take the weight?




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