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Question on my image size

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18 replies to this topic

#1 JimNaySeeUm

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Posted Yesterday, 09:29 AM

Went out last night for some planetary imaging, poor seeing conditions.  But I was excited to try a new Barlow.  I used a 2x Explore Scientific (listed as more of an extender like a powermate). I had been using a inexpensive GSO 2x Barlow.   Hoping the better optics might help for imaging, again can't really compare because of the poor seeing last night.

 

My question is I noticed my captured images were considerably smaller with the new 2x extender than they were with the 2x barlow.  I thought 2x was 2x.   Any thoughts on why they would be smaller.  The first pic was taken last week with my GSO barlow and the second one was last night.  

 

This comparison does also give the difference between good and bad seeing conditions.

Attached Thumbnails

  • 2020-07-25-0517_7-RGB-Jup_#2 Exposure=3.jpg
  • 2020-08-02-0713_2-RGB-Jup_Exposure=4.jpg

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#2 Toddeo

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Posted Yesterday, 09:35 AM

I have noticed the same thing. I have over a half dozen barlows/extenders from 1.5x to 3x mag. Everyone is different. The closest that is correct seems to be my Tele Vue barlows. I definitely  think that my Explore Scientific Extenders are way off! Like your photos show- the ES 2x looks almost like only 1.5x.



#3 sg6

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Posted Yesterday, 10:37 AM

Suppose the question is: Whatever makes you think that one 2x equals another 2x?  lol.gif  lol.gif  lol.gif

This astronomy don't you know, where no rule is actually a rule, just a guideline. foreheadslap.gif

 

As the result is dependant on the separation of barlow from objective and the focal length of the objective there is a good chance that one was initially designed and built with a different scope/objective/separation in the parameters. So a different end result.



#4 JimNaySeeUm

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Posted Yesterday, 12:29 PM

Thanks for the reply's, I think I will send this one back in.  I was getting fine images with my GSO, maybe I can swap the Explore Scientific for a 2.5x or 3x in another brand.  

 

Any suggestions?  Thanks



#5 Tapio

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Posted Yesterday, 12:45 PM

How about changing camera distance from barlow/extender ?



#6 JimNaySeeUm

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Posted Yesterday, 12:57 PM

Tapio, 

Right now I have it set up in this order:

 

Barlow, ADC, ZWO 224

 

You suggest flipping the ADC and barlow?  I thought I read this doesn't really change with the Extenders.



#7 Tapio

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Posted Yesterday, 01:05 PM

It seems that at least PowerMates hav some variation:
http://www.televue.c...?id=53&Tab=_app



#8 JimNaySeeUm

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Posted Yesterday, 03:47 PM

Tapio, 

I will play with the placement and seeding of the barlow.  Thanks



#9 pastorgalactico

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Posted Today, 11:58 AM

Hello;
And you thought maybe the GXO barlom X2 might give you 2.5X.
The GSO if the camera and lens separation is modified barlom changes the X's and yet Explorer X2 I think that it does not modify the X's if it is separated more.
Regards.

#10 GeorgeInDallas

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Posted Today, 12:16 PM

TeleVue barlows also have a significant variation in magnification depending on placement. I would guess that other manufacturers Barlows have similar variation. 

http://www.televue.c...d=52&Tab=_photo

 

 

BTW, the top image is pretty spectacular if you took it from Kansas. I would stick with that Barlow if I were you.

 

George


Edited by GeorgeInDallas, Today, 12:20 PM.

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#11 JimNaySeeUm

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Posted Today, 04:56 PM

Thanks everyone,

I am fairly new to this hobby and somewhat dense on what you all are try to tell me, but I think I might be on to something.

 

On both images the first with my GSO 2x barlow and the 2nd with the Explore Scientific 2x barlow, were set up the same.  Barlow, ADC, Camera.  

 

Now the Explore Scientific is longer.  So the distance of the camera from the scope increased to 5 3/16" with the Explore Scientific.  The distance was only 4 1/2" with the GSO.

 

So "captain dumb here," does moving the camera further back from the scope reduce the magnification?


Edited by JimNaySeeUm, Today, 04:58 PM.


#12 Dunkstar

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Posted Today, 05:32 PM

It may be that way with the ES (the 2.5x PowerMate is much the same) but with conventional Barlows the further you move the sensor from the Barlow lens itself, the higher the magnification becomes.



#13 KTAZ

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Posted Today, 05:59 PM

This is an interesting conversation.

 

I also use a Barlow and ADC for planetary imaging (VB > Barlow > ADC >Cam). I have a Tele Vue 2x, by the way, which I am very happy with. Don't put anything but quality in your optical train. YMMV.

 

I was surprised to see FireCapture calculate my FL as 6000 the night before last! I had never noticed this in the txt file generated with my AVI, so I was a bit shocked since it should have been closer to 4700. Since my pixel size is 3.75, I should be shooting for f/18.75 or so, 20 would be fine, but at 6000 FL I am closer to f/25.5! Based on what I've read, that would be way over the "theoretical" Barlow bump that I should be pursuing (pixel size x 5). It seems pretty clear that the ADC is driving up my magnification due to the additional separation between the Barlow and camera chip.

 

So, the next time the bloody smoke from the Apple Fire clears, I am going to try a few modifications; 1) I will push the barlow into my visual back all the way to the rear of the SCT plate to reduce the magnification, 2) I will swap the ADC and the Barlow to see what effect that has on magnification as well (presuming that placing the Barlow after the ADC will still put the Barlow lens within the focal plane).

 

I am curious to see what numbers I get. I'd hate to have to buy a 1.5x Barlow to get better images. But logically, Barlows should be closest to their specified magnification at the top of the Barlow tube.


Edited by KTAZ, Today, 06:01 PM.


#14 JimNaySeeUm

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Posted Today, 06:00 PM

Dunkstar, 

So with a regular Barlow moving the camera further away should have increased my magnification not decreased it.  



#15 KTAZ

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Posted Today, 06:06 PM

That is correct.



#16 KTAZ

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Posted Today, 06:08 PM

Tapio, 

Right now I have it set up in this order:

 

Barlow, ADC, ZWO 224

 

You suggest flipping the ADC and barlow?  I thought I read this doesn't really change with the Extenders.

The only difference with an extender versus a Barlow is it does not effect eye relief.



#17 GeorgeInDallas

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Posted Today, 06:43 PM

I might make a comment about the FireCapture focal length calculation. I went through this recently and as I understood Torsten ( the FireCapture author) to say, the planet needs to be oriented properly in the camera FOV for the reported focal length to be approximately correct +/- 5%.

 

I hope this is useful.

George


Edited by GeorgeInDallas, Today, 06:44 PM.


#18 Dunkstar

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Posted Today, 06:44 PM

Dunkstar, 

So with a regular Barlow moving the camera further away should have increased my magnification not decreased it.  

With a regular Barlow, correct! But more sophisticated extenders like the ES and TV Powermate don’t follow this since they are a different optical design.

 

With a conventional Barlow, moving the sensor closer to the Barlow lens reduces the magnification... that’s not to say it reduces below 1.0x, it doesn’t, but it means you can somewhat tune your optical train accordingly. Note that this assumes decent optical quality, and all bets are off for a $10 Barlow lol.gif



#19 Kokatha man

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Posted Today, 08:36 PM

You might like to read through ALL of this thread to get the salient points..!!!

 

https://www.cloudyni...more-power/      




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