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102mm to 127mm : only 0.2" ; is it noticeable ?

astrophotography solar
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#1 chrishalpha2017

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Posted 02 June 2020 - 11:15 PM

hello ,

 

I have a question for the whole solar observers group :)

 

I'm currently using a Bresser Messier refractor 102/1350 with should give max resolution of 0.8"  (depending on the formula one use to calculate it).

 

and I'm tempted to go for the Bresser Messier refractor 127/1200 with would allow to reach 0.6" resolution .

 

There is only a slight difference of 0.2" !! will that be visually noticeable ?? will I see some interesting gain in imaging ?? ( turbulence problems put aside)..

 

Is it worth the purchase ? I expect a gain in light gathering and hence a brighter image.

 

You 've got to bare in mind that i'm only watching the solar prominences on the limb and only on  the very small portion that is visible through the entrance slit of my spectroscope.

 

I'm only considering  the prominences observation in this matter.

 

What do you think ?

 

I'm also asking you this question because i was striked by the sharpness and contrast provided in h alpha by the 102/1350 !  Will i get the same with the 127/1200 ?

 

thanks a lot in advance.

 

Chris

 



#2 TOMDEY

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Posted 03 June 2020 - 02:43 AM

Chris, I'm assuming you are optimally-scaling your optomechanical slit width to the angular resolution limit (Rayleigh, Dawes, Sparrow, other) of your scope. In that case, the scope is optimized both spatially and spectrally. You can, of course play spectral against spatial resolution (they are both coherence considerations... spatial resolution relates to image sharpness, spectral res is longitudinal, in the direction that the light travels). Emmy Noether's Invariance Theorem assures that , after all the dust settles, the bigger scope is better, by the square of its aperture. So the 127 is potentially (5/4)2 = 1.56 times better than the 102, in terms of information throughput. How you avail and parse that surplus information capacity is up to you: Better spatial resolution, better spectral resolution, or some combination.    Tom


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#3 chrishalpha2017

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Posted 03 June 2020 - 03:07 AM

Hello,
Thank you for the answer a lot.
The technique i use is the WIDE slit spectroscope to image the whole prominence in one bit , so there is no diffraction problem due a slit that would be too narrow like in the case of a soectroheliograph. So i wanted to know if visually i would notice an improvement .

#4 MalVeauX

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Posted 03 June 2020 - 07:12 AM

Heya,

 

The resolution difference is significant, however, the demand on seeing is also significant. I'd say go for it.

 

The difference in 0.2" resolution however is not just slight. That's a lot. To make a relative example, going from 0.5" to 0.3" is also just 0.2" but that's a monstrous difference in what it takes to achieve that (and seeing conditions to even benefit it).

 

Very best,


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#5 spatzek

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Posted 03 June 2020 - 11:45 AM

The Bresser 127mm is a great telescope. I have used it with a Quantum filter and a 2.5x Powermate. I had the "normal" 102mm Bresser and hands down, the 127mm is much better on the Sun.


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#6 chrishalpha2017

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Posted 03 June 2020 - 11:47 AM

thank you very much!! i wasnt realizing the advantage it could be as I have a Bresser Messier 102/1350 and already a Frehel (Celestron copy)  120/1000.

 

The thing is that my 120/1000 is a rather average quality  and quite low compared to my 102/1350. So I guess if the quality of the Bresser 127/1200 is the same then I will be able to better see structures like the spicules wich i could already see with the 102/1350 ; but I guess at least they will bee better resolved when the seeing is good enough.

 

I'll give a feedback as soon as I can test it in h alpha.

 

 

So ; a huge thank you to you guys for the answers.


Edited by chrishalpha2017, 03 June 2020 - 11:52 AM.


#7 old_frankland

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Posted 05 June 2020 - 11:35 AM

Another consideration is more light to the camera which allows higher shutter speed....depending on the f/ratio you settle upon with the 120m scope.



#8 ValeryD

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Posted 05 June 2020 - 12:09 PM

Even more to consider.  Instead of a new 127mm refractor better buy a used 150mm.

You always can stop down the aperture to 127mm or even to 100mm if the seeing does not support the resolution.

However when the seeing is OK,  with a 150mm aperture you will see prominences in their full glory.  Phenomenal !!!

For example,  today I observed the sun visually with two my Quarks. The seeing was good from about 9:00 to 14:00.  I observed two active areas (with spots in the second one) with narrow Quark Chromosphere and then I observed prominences at north-east limb with my second Quark (which is very bright) at  180 to 220x.  Fantastic.  With smaller aperture 111mm the views were not as impressive.  Big difference!   With achromats for H-a observing an investment in aperture is the best possible investment.

 

 

Valery


Edited by ValeryD, 05 June 2020 - 12:09 PM.

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#9 chrishalpha2017

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Posted 05 June 2020 - 01:54 PM

i wanted to buy the bresser 152/1200 but there is a big issue : its weight !! far too heavy for my EQ5 mount ; and when I add my spectroscope its even worse!

so the best compromise was the Bresser 127/1200



#10 chrishalpha2017

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Posted 06 June 2020 - 11:50 AM

Hello Valery,

I dont earn much money and a good mount is far too expensive for me ; plus H alpha filters are very expensive. Not all of us can afford that .

 

At the time some 20 years ago i bought the Lumicon H alpha filter 1.5A and was quite happy with it but within a few years the contrast started to décrease and I was already looking for a substitute method. Moreover , i'm fascinated with the pionners experiments and discoveries. Hence I reproduced Roentgen experiment in producing Xrays with a home made vacuum cathodic rays tube with a genuine radioscopic fluorescent in the dark screen. That was magical when it started to work..

 

I also reproduce the Denis GABOR experiment on first holograms with  the first laser pointer (1998) and it was magical to see my first homemade hologram recorded on standard B&W film..

 

And Then I found out abour JANSSEN and SECCHI  and decided to reproduce the experiment as nobody had tried and took proper photos with that method. ...and i've been working with it for the last 20 tears and I still love it.

 

I also wanted to show other amateur that solar prominence observation doesnt have to be expensive when you are patient :)

 

But i you buy me an h alpha filter I will be pleased of course ;)

 

chris ;)


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