Barlow for astrophotography

[Calzune]

Is it possible to use a Barlow2x-5x 2" for AP? 

[carastro]

You can use one for planetary imaging.  Deep sky imaging with long exposure has always been a NO NO, due to the reduction in focal ratio, but I have heard an exception to this at one point, but in general I don;t think people do use a Barlow for long exposure imaging.

Carole 

[Calzune]

Just now, carastro said:

You can use one for planetary imaging.  Deep sky imaging with long exposure has always been a NO NO, due to the reduction in focal ratio, but I have heard an exception to this at one point, but in general I don;t think people do use a Barlow for long exposure imaging.

Carole 

Okey thanks

[CloudMagnet]

Agree with above. I used to image for a while at 2000mm focal length for deep sky stuff and it was difficult to say the least. The more magnifcation you have means your tracking has to be perfect or you will get star trails very quickly. Keep in mind the reduction in focal ratio means darker images, which in turn needs longer exposures to compensate, putting even more pressure on tracking.

My advise is keep the magnification as low as possible for deep sky as this is much more forgiving.

[Aramcheck]

On 20/11/2019 at 19:02, CloudMagnet said:

My advise is keep the magnification as low as possible for deep sky as this is much more forgiving.

Does this apply for imaging with an 8" newt & DLSR? I'm extremely new to astronomy/photography so was thinking of getting a barlow as the first couple of images I took (M57 & M27) were quite small in relation to the picture size with a Canon EOS-600D.

I presume it's the accuracy of the tracking that creates the problem?

Cheers
Ivor

[Erling G-P]

2 hours ago, Aramcheck said:

Does this apply for imaging with an 8" newt & DLSR? I'm extremely new to astronomy/photography so was thinking of getting a barlow as the first couple of images I took (M57 & M27) were quite small in relation to the picture size with a Canon EOS-600D.

I presume it's the accuracy of the tracking that creates the problem?

Cheers
Ivor

It is indeed.  I have a Skywatcher 200PDS (8" Newton), using it unguided so far on a HEQ5Pro, with a Nikon D7000.  Like you I have also found M57 to be very small, and have tried a couple of times to use a 2x Barlow.  Shooting unguided, I have limited myself to 30-sec exposures, but with the Barlow, I had to discard them all, due to tracking errors being blown up.  Finally got something somewhat useful, by going down to 15-sec exposures.  Below are two cropped versions of this; the first have used less subs, while I included more, lower quality ones for the 2nd.  As you can see, the 2nd perhaps looks nicer regarding the nebula, but is definitely more fuzzy.  Reason for the smaller central star, is using 'Reduce stars' feature of Astroart.

[CloudMagnet]

7 hours ago, Aramcheck said:

Does this apply for imaging with an 8" newt & DLSR? I'm extremely new to astronomy/photography so was thinking of getting a barlow as the first couple of images I took (M57 & M27) were quite small in relation to the picture size with a Canon EOS-600D.

I presume it's the accuracy of the tracking that creates the problem?

Cheers
Ivor

I use the Skywatcher 200p with a DSLR as well. I started imaging with a Barlow which just makes any tracking twice as difficult as the more you zoom in towards the stars, the faster they appear to move and the quicker any errors will show in any picutres.

You may come across something known as the "rule of 500". This gives you an estimate of how long you can take an exposure before star trails appear. It is calculated by taking 500 and dividing by your focal length. For example my telescope has a 1000mm focal length so for me: 500/1000 =0.5seconds. So I can only take a 1/2 second exposure before star trails appear. If I add the barlow and double my focal length to 2000mm, then this reduces the time before stars trail to 0.25 seconds.