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Achromats for video

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#1 Atl

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Posted 30 January 2016 - 11:28 PM

I have been playing around with a small refractor lately...an ETX70. I last used a refractor in 1976 when I was 11. It was a Tasco 60mm. I could barely find the moon with it. So, I was surprised that the fast ETX gave really good views for what it is. It made me curious about doing video with a larger fast refractor. Before comet Ison fell into the Sun Explore Scientific was brought a f4.5 102mm achromat to market as the Comet Catcher. I don't know what they charged. After Ison fizzled they packaged it as a package deal like this one with binoculars and an AZ mount for $475. Lately to get rid of stock they dropped it to $250 so I bought the set. The scope is prob crap since it is so large and fast and the mount is likely crap also. The binoculars get good reviews at $86 on Amazon. However Explore is a generally good company...I have some alright inexpensive eyepieces from them so just maybe the OTA will be passable for light video. I found no reviews good or bad for it. I would love to own a 6" Apo but the money is not quite there for that yet. Anyone have advice for using large fast achromatic refractors for video?



#2 Censustaker

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Posted 30 January 2016 - 11:36 PM

Ken James gets great results with fast achromats. The best tip he gave me was to use a yellow 12 filter. I own a 102mm ES AR102 achromat that I use now and then and it's great. Nice sharp stars, wide view, not too heavy, great price. I posted a video yesterday of the revolution imager in this scope using a manual mount to view m42: https://youtu.be/0pAzxR3OsA0


Sorry, forget to mention: the yellow filter is to prevent the purple fringing you see with fast achromats. Works like a charm

Edited by Censustaker, 30 January 2016 - 11:37 PM.

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#3 Dwight J

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Posted 30 January 2016 - 11:55 PM

I would think about an infrared blocking filter as well.  It keeps the stars tighter at the loss of a bit of sensitivity.  If you plan on using a light pollution filter get one that blocks IR too.  IIRC the IDAS filters do just that.  



#4 Dragon Man

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Posted 31 January 2016 - 06:20 AM

Atl, both posts above are correct.

 

I use large and small fast Achromats for my Video Astronomy and with the simple addition of a #8 or #12 yellow filter and a good IR cut filter Achromats works great.

No more Violet Fringing or Chromatic aberration   :waytogo:  

 

See my tests here: HERE


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#5 nytecam

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Posted 31 January 2016 - 07:28 AM

I had a number of ETX-70 scopes given by a dealer and donated them to local schools and club members but got little feedback. 

 

The samples that I kept work fine both visually and in EAA with Lodestar and SX-Mx2 cameras - mostly demounted and piggybacked on my SCT. Here's M51 via the scope mount in 24x5s exp. Check my ETX DSO gallery via link below for more.

Nytecam

Attached Thumbnails

  • 2497585-m51etxlod080702.jpg

Edited by nytecam, 31 January 2016 - 11:35 AM.

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#6 GlennLeDrew

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Posted 31 January 2016 - 08:40 AM

I used an 80mm f/5 achro with a Mallincam MFR-5 focal reducer; the result being an 80mm f/2.5. I used an Orion light pollution filter for imaging, and got great results on the larger DSOs.


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#7 Atl

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Posted 05 February 2016 - 12:51 AM

I ordered the recommended #8 yellow and ir cut filters. Thanks for the advice all. Does anyone know if the yellow filter is useful for visual as well to reduce CA?



#8 Dragon Man

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Posted 05 February 2016 - 01:16 AM

Yes, it works for visual too Atl. It may give a slight yellow tinge to some objects, but you don't really notice it.

It will actually make your view look even better by increasing contrast.

 

Just remember that if you go up in size, like to a 6" f5 Achromat you will need the stronger #12 yellow.

 

But at only about $19 it's not a problem  :)



#9 Dwight J

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Posted 05 February 2016 - 01:16 AM

I ordered the recommended #8 yellow and ir cut filters. Thanks for the advice all. Does anyone know if the yellow filter is useful for visual as well to reduce CA?

 

Yes, it works for visual too.  It will add a colour cast but it also improves contrast.  



#10 Atl

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Posted 05 February 2016 - 07:38 AM

Thanks. If I move up I will spring for the #12. I have seen them as cheap as $10 so no issue there.



#11 Atl

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Posted 09 February 2016 - 10:28 PM

I received the 102mm refractor (mentioned above) yesterday. It is a fairly high quality setup it seems. The scope can be collimated and also came slightly out of collimation. After spending a few hours playing with the collimation screws I took it outside tonight for a star test on SIrius. There is some CA, but much less than I was reading I would see. It is an f4.5 scope with a 459mm focal length. I think the scope itself was worth the money, but the mount and binoculars are decent. The included 70 degree 20mm eyepiece is actually pretty awesome. Haven't had a chance for video, but I soon will put it to that test. I have the yellow and I filters as well set to go. The scope should be a no brainer for video.



#12 Dragon Man

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Posted 09 February 2016 - 10:36 PM

We look forward to a report on the results Atl.  :)



#13 Atl

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Posted 09 February 2016 - 11:31 PM

Thanks. I will give it my best shot! For those that like small technical details the Bresser 102mm Comet Edition optical tube weighs 6.4 pounds with the lens cover on. It is pretty light (and short) for a 4" refractor.



#14 Dwight J

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Posted 10 February 2016 - 12:39 AM

Looking forward to your results there Atl.  That is a real lightweight.  Sweet focal length too and no reduction needed.




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