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Nikon D750 Refractors Acquisition Beginner Deep Sky
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Yogs avatar
Yogs avatar
Hi Everyone,

I am new to Astrophotography. I love the photos and decided to join the hobby.
I have a full frame Nikon D750 camera, and I have ordered Explore Scientific 102mm triplet.

Few questions to get me started please:
1. Do I need to use extension tube to connect my camera to help focus (I have t-ring and T2 focal adapter to connect to telescope)?
2. For close-up moon photography, do I need to connect my camera to eyepiece via diagonal?

thanks in advance.

Yogs
Pablo Petit avatar
Pablo Petit avatar
Hello Yogs, and welcome to this amazing hobby !

To answer your two questions : 

1/ In order to have round star all over the field with a refractor, you will need the apropriate field flattener, that sometimes also doubles as a reducer. Once you have that, you will have to have a certain distance between the end of the reducer and your sensor (which is almost always 55mm and is called backfocus). It is usually simple to acheive the 55mm with a DLSR, most parts are made to give that amount of backfocus.

2/ In don't see a case where a diagonal would help you as it just adds an unecessary mirror in your light train that will only disturb your images. You might need a barlow to get more focal lenght for the moon thought. 


Hope this helps
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Yogs avatar
Yogs avatar
Pablo Petit:
Hello Yogs, and welcome to this amazing hobby !

To answer your two questions : 

1/ In order to have round star all over the field with a refractor, you will need the apropriate field flattener, that sometimes also doubles as a reducer. Once you have that, you will have to have a certain distance between the end of the reducer and your sensor (which is almost always 55mm and is called backfocus). It is usually simple to acheive the 55mm with a DLSR, most parts are made to give that amount of backfocus.

2/ In don't see a case where a diagonal would help you as it just adds an unecessary mirror in your light train that will only disturb your images. You might need a barlow to get more focal lenght for the moon thought. 


Hope this helps

Thanks Pablo! This is helpful.
In regard to flattener/reducer, won't that degrade the quality as my camera is full frame and crop sensor?

thanks,
Yogs
Pablo Petit avatar
Pablo Petit avatar
No actually it will be the opposite, without a flattener your stars will become elongated the farther they are from the center, and look like this :


And because a full frame is a big sensor you will notice it even more. Now, it might be possible to have some vignetting because of the flattener on a full frame, but overall, a flattener will be a good investement.
Also, if i'm right the flattener you will have to buy for your ES 102mm is this one :
https://www.bresser.de/fr/Astronomie/Accessoires/Correcteurs-Reducteurs/EXPLORE-SCIENTIFIC-3-0-7x-Reducteur-Correcteur.html
Which is also a 0.7 reducer that will bring your focal ratio from 7 to 4.9 and will reduce your exposure time by 2, which is a lot, so its a big advantage.
Helpful
Yogs avatar
Yogs avatar
Pablo Petit:
No actually it will be the opposite, without a flattener your stars will become elongated the farther they are from the center, and look like this :

And because a full frame is a big sensor you will notice it even more. Now, it might be possible to have some vignetting because of the flattener on a full frame, but overall, a flattener will be a good investement.
Also, if i'm right the flattener you will have to buy for your ES 102mm is this one :
https://www.bresser.de/fr/Astronomie/Accessoires/Correcteurs-Reducteurs/EXPLORE-SCIENTIFIC-3-0-7x-Reducteur-Correcteur.html
Which is also a 0.7 reducer that will bring your focal ratio from 7 to 4.9 and will reduce your exposure time by 2, which is a lot, so its a big advantage.

Thank you again Pablo! Good to understand the stuff. I will get a reduce/flattener to start getting good pictures.