Deep sky imaging magnification

[choochoo_baloo]

I am considering buying a quality Barlow to allow me to collect enlarged views of the smaller deep sky targets e.g. the Pinwheel Galaxy. It would be attaching to a William Optics Gt-81 refractor. I realise that multiplying up focal length increases the f/stop and thus exposure times.

Is it worth considering, or are multipliers (Barlows, Powermates etc.) a real no go for short and fast refractors like this due to deterioration of other factors?

If it is feasible; aside from TeleVue, what other top drawer brands would people recommend for imaging grade focal multipliers?

Thanks.

[datman]

Hi

You might get a better response if you did a basic proof read on your post. I'm assuming key = sky.

You don't mention what other equipment you are using, I've checked your website and see an EQ3-2, Nikon DSLR and a SW150.

A 2x barlow/Teleview will double your exposure time so for the Pinwheel maybe 10 minutes @ iso 400/800

IMO the Eq3-2 isn't anything like sturdy enough for this length of exposure, especially since it would need to be guided.

Is that why you're not using the SW150P? @ F5 It would have much better light grasp and @ 750mm isn't too bad for DSOs.

If you are using both as a guided set up, they a much too heavy for the EQ3-2. The slightest wind or vibration will wreak any long exposures

The refractor + DSLR will give what seems to be a very small image of the galaxy, but if you where using a 1/2" ccd the image would look like this;

Although your DSLR ccd is much larger, it's pixel size 5.5 is not that much different to the 1/2" sensor. The orient is 8.3 but the image with a QHY5 (5.6)  is very similar.

As you can see the pinwheel fills the 1/2" ccd quite well, so if you cropped the DSLR image, it would be of a similar quality to the 1/2" sensor.

Before you spend lots of money on a Teleview, try the refractor on it's own, but with an Eq3-2 you're definitely over the edge!

Buying a much sturdier tripod/mount would be a better Investment.

If you really want to keep the EQ3-2, try a 500mm camera lens (you might get away with less e.g. 250mm) as the quide scope. They aren't as easy to focus and you'll

need an adaptor to fit the camera but they are much lighter. I used a 500mm lens until I bought an HEQ6.

[ollypenrice]

If all you needed to do to use a small scope for small-object imaging was pop a Barlow in the train then, believe me, the DS imaging boards would be brimming with images so captured. But they are not. 

Datman, surely putting a 2x Barlow in the line won't double the exposure time, it will quadruple it, no?

This would be dismally slow and require the kind of exposure times which neither a budget mount nor an uncooled DSLR will support.

In short we never see it because it doesn't work.

Olly

[Tinker1947]

Its not a cheap route doing AstroP, but it does require a good mount, something like a HEQ5, the scope for deep sky would need to be fast'ish and have a long'ish focal length so maybe a newt would fit in here to start with 150mm and a DSLR Canon to image with, others will add there preferred set-up but pixel for pound i believe my list is the cheapest route.....

[datman]

If all you needed to do to use a small scope for small-object imaging was pop a Barlow in the train then, believe me, the DS imaging boards would be brimming with images so captured. But they are not. 

Datman, surely putting a 2x Barlow in the line won't double the exposure time, it will quadruple it, no?

This would be dismally slow and require the kind of exposure times which neither a budget mount nor an uncooled DSLR will support.

In short we never see it because it doesn't work.

Olly

Yes Olly you're right, too early and too old is my excuse ;-)

[lensman57]

I am considering buying a quality Barlow to allow me to collect enlarged views of the smaller deep sky targets e.g. the Pinwheel Galaxy. It would be attaching to a William Optics Gt-81 refractor. I realise that multiplying up focal length increases the f/stop and thus exposure times.

Is it worth considering, or are multipliers (Barlows, Powermates etc.) a real no go for short and fast refractors like this due to deterioration of other factors?

If it is feasible; aside from TeleVue, what other top drawer brands would people recommend for imaging grade focal multipliers?

Thanks.

Forget this idea, it is most impractical. You are best using your DSLR and crop the image. For going really deep you'd need long FL, fast Fratio and perfect guiding on a solid mount and all these add up to a lot of money.

Regards,

A.G

[choochoo_baloo]

A 2x barlow/Teleview will double your exposure time so for the Pinwheel maybe 10 minutes @ iso 400/800

It is a square relationship between exposure time and focal magnification, so quadrupled not doubled. 

Hi

You don't mention what other equipment you are using, I've checked your website and see an EQ3-2, Nikon DSLR and a SW150.

A 2x barlow/Teleview will double your exposure time so for the Pinwheel maybe 10 minutes @ iso 400/800

IMO the Eq3-2 isn't anything like sturdy enough for this length of exposure, especially since it would need to be guided.

Before you spend lots of money on a Teleview, try the refractor on it's own, but with an Eq3-2 you're definitely over the edge!

Buying a much sturdier tripod/mount would be a better Investment.

Thanks for the advice. I agree with all of this; I should have mentioned my other planned purchases in addition to the William GT-81:

Celestron Advanced VX mount

Rear filter removed Canon D500 (after speaking to an expert DSLR imager I now know that my lovely Nikon will have to remain a daytime interment only for a number of reasons  )

Orion Shorttube 80 as guider

The QHY5L-II I already own as guiding camera

Both scopes mounted side-by-side using one of the ADM Vixen thingys - lower centre of mass than trying to piggy back on the small GT-81

Does this all sound like a good/future-proof set-up to set me up on my way to some serious imaging?

Forget this idea, it is most impractical. You are best using your DSLR and crop the image. For going really deep you'd need long FL, fast Fratio and perfect guiding on a solid mount and all these add up to a lot of money.

Regards,

A.G

Thanks also. Having mentioned the other planned items (see above), is it still the case that the GT-81 is a no go with some type of focal magnification?

[Scott]

Hi

You might get a better response if you did a basic proof read on your post. I'm assuming key = sky.

You don't mention what other equipment you are using, I've checked your website and see an EQ3-2, Nikon DSLR and a SW150.

A 2x barlow/Teleview will double your exposure time so for the Pinwheel maybe 10 minutes @ iso 400/800

IMO the Eq3-2 isn't anything like sturdy enough for this length of exposure, especially since it would need to be guided.

Is that why you're not using the SW150P? @ F5 It would have much better light grasp and @ 750mm isn't too bad for DSOs.

If you are using both as a guided set up, they a much too heavy for the EQ3-2. The slightest wind or vibration will wreak any long exposures

The refractor + DSLR will give what seems to be a very small image of the galaxy, but if you where using a 1/2" ccd the image would look like this;

Although your DSLR ccd is much larger, it's pixel size 5.5 is not that much different to the 1/2" sensor. The orient is 8.3 but the image with a QHY5 (5.6)  is very similar.

As you can see the pinwheel fills the 1/2" ccd quite well, so if you cropped the DSLR image, it would be of a similar quality to the 1/2" sensor.

Before you spend lots of money on a Teleview, try the refractor on it's own, but with an Eq3-2 you're definitely over the edge!

Buying a much sturdier tripod/mount would be a better Investment.

If you really want to keep the EQ3-2, try a 500mm camera lens (you might get away with less e.g. 250mm) as the quide scope. They aren't as easy to focus and you'll

need an adaptor to fit the camera but they are much lighter. I used a 500mm lens until I bought an HEQ6.

As you find it necessary to point out other peoples errors, I assume you mean wreck rather than wreak. To my knowledge, wind has never caused any long exposures. Just something to think about

[ollypenrice]

I wouldn't bother with side by side myself, but that's a detail. I piggyback with small setups, provided the imaging scope has tube rings. If you have just a shoe go side by side. It's no big deal either way but you can track longer past the meridian with a piggyback because, being narrower, it collides later with the mount. It is also marginally easier to balance. But no ig deal.

Olly

[choochoo_baloo]

Thanks Olly, I may well switch to piggybacking now since you explained the reasons in support of it.

[datman]

As you find it necessary to point out other peoples errors, I assume you mean wreck rather than wreak. To my knowledge, wind has never caused any long exposures. Just something to think about

Well it would seem I was right, and at least I took the trouble to provide some advice.

Criticism alone is easy, constructive feedback takes some thought.

[Scott]

Well it would seem I was right, and at least I took the trouble to provide some advice.

Criticism alone is easy, constructive feedback takes some thought.

I fail to see how you think your condescending opening to your reply was right or even needed with your reply.

There are ways to point out an error and then there is the way you chose.

Still, you're obviously happy with the way you address members even though it seems unacceptable for us to point out your errors so carry on.....for now

[choochoo_baloo]

I am sorry that an innocent mistake of one word has caused this. 

To put the record straight:

datman - it is a shame you opened what was otherwise a very helpful post with an unnecessary/aggressive sentence. I would not speak to a complete stranger on a forum in that manner - I *did* skim read it and must have missed that so apologies for being human. Anyway I wish to reitorate, it was otherwise a very useful post thank you.

auspom - Thank you for intervening earlier on. I agree with you that it was unnecessary conduct from the other chap and it is pleasing that the moderating team uphold strict courtesy on this excellent website. I don't wish to cause a nuisance to anyone (not that I did in the first place!) so it's fine with me to move on; I think that the chap has learnt to stop and think in future a tad more.

[choochoo_baloo]

It's all cool with me now datman. Please just leave it - don't dig yourself a hole.

I'll say it again: your initial post was very informative.

[lensman57]

it just does not

It's all cool with me now datman. Please just leave it - don't dig yourself a hole.

I'll say it again: your initial post was very informative.

I too make a lot of spelling mistakes in my posts for different  reasons. My HP laptop has developed the sticky cursor disease and  has a mind of its own at times it deletes letters and jumps all over the place at times it just does not respond to key inputs and as a result a post that should take less than 30s to complete takes me two minutes as I have to go back and check it all. I work in the evenings so most of the time I am just too tired to go back and forth in my posts and mistakes happen. No big deal but at  times I really get angry with this stupid machine. In this short reply I had to correct for missing letters, omitted words and some of the reply was written in the "quote " above. All hail Win7 64.

Regards,

A.G