Can you use a normal Frac for imaging ???

[Purplehayze104]

hi all

bit bored as raining & miserable, i was wondering, if you could use a normal refractor for imaging, i know there is C.A with these scopes, would if affect DSO's much & could you sort of get round it with a ccd & filters ?

[JamesF]

Such as your Evostar? Or were you thinking of another scope?

It's certainly possible. If you search for images in the DSO section posted by "stan26" you should find some taken using an ST102 (if I'm remembering right).

James

[ronin]

Suspect the 90 would be fair, the 70 not so.

Would need a fairly well set up equitorial mount and the exposure time would need to be on the shorter side so in effect lots of short duration exposures.

CA would be present, but on DSO's minimally, more on Moon, Jupiter, Saturn and say the Pleiades.

Filter would reduce it but also reduce other things so little or no advantage I would guess.

CCD will detect CA as well as any other sensor, it is just light in the wrong place.

[JamesF]

Meant to add, yes, you can deal with CA using filters to a certain extent. You almost certainly would need to refocus between filters though.

James

[Purplehayze104]

yeah was thinking of using the evo 90 maybe with a .5x reducer to shorten focal length be interesting to see some results would love an ED but will have to go on the wishlist for a while

[Purplehayze104]

just had a look at stan26 effort thru his 102 an was impressive if i even got anywhere near that id have a big smile (think will give it a go near future)

[RikM]

You can get away with quite a lot using a CCD with a small chip, narrowband filters and a bit of patience.

[LukeSkywatcher]

I agree. With the 90mm scope you have a better chance. The travelscope with its wobbly tripod is a non-starter. Short exposures (and lots of them) with the 90mm then stacked should give some result. Moon and planets will be easier.

Why not use the 150mm on the EQ3-2 PRO?

[ollypenrice]

yeah was thinking of using the evo 90 maybe with a .5x reducer to shorten focal length be interesting to see some results would love an ED but will have to go on the wishlist for a while

Not a chance. Your forum name says it all! Purple haze is what you'd get! The 0.5 reducer is intended for tiny chips in slowish telescopes. You can give the unreduced achromat a whizz and get the hang of imaging but you will soon want a semi apo or apo. On a low budget Newts easily beat achromats.

Olly

[steppenwolf]

By all means use the 90 to get some practice in but you will be disappointed in the end. Two features of an achromat will show themselves - elongated stars at the periphery (but this affects APOs as well) and the chromatic aberration that you have already identified. The former can be resolved with a field flattener/focal reducer but a .5 FR will not have this correction built in. Using a one shot colour camera like your D3100 will show up both these defects heavily although you could use a minus violet filter to remove the halos or attack these in post processing but the result will be a little bit of a kludge.

A small mono sensor CCD and filters would help although you would have to adjust focus at every filter change (I do this anyway even with my APO just to be sure) so you could capture reasonable red and green with a poorer blue channel BUT the most important channel, the Luminance on which the overcoat of colour would be laid in post processing would not be good because it would be capturing all the wavelengths of light at once (albeit in mono) and your stars would suffer from bloat because of this.

You are really attacking the 'problem' from the wrong angle as, sadly, there are no really satisfactory shortcuts when it comes to imaging. Once you have tackled the mount (you need a solid equatorial mount) you could start using your 150P and DSLR in earnest while you start filling the piggy bank to get at least an ED refractor. Even with the 150P you would need a coma corrector.

All of that said, get out there and have a go, you'll have fun and learn plenty in the process.

[Purplehayze104]

thanks for all your reply's on this subject certainly cleared a few things up, i do use the newt more than the 90 (will stick to visual i think with the 90), have a bit of trouble with focus on the newt as with Nikon there's no real software that i can use to connect it up to a pc a see the liveveiw, so most of time i end up with donuts gets a bit frustrating, in DSS "computer says nooo"

[laser_jock99]

To some extent CA can be processed out of an image in software. It just depends on how much you are prepared to put up with in the final image.

It's easier to loose the CA haloes from around the smaller stars, big blue haloes are more tricky. But if you already own the scope there is no harm in giving it a go.

The image below was taken with a 'semi apo' achromat (i.e. not as well corrected as it should have been!) but I did 'loose' some of the CA in Photoshop.

[RikM]

To some extent CA can be processed out of an image in software. It just depends on how much you are prepared to put up with in the final image.

It's easier to loose the CA haloes from around the smaller stars, big blue haloes are more tricky. But if you already own the scope there is no harm in giving it a go.

The image below was taken with a 'semi apo' achromat (i.e. not as well corrected as it should have been!) but I did 'loose' some of the CA in Photoshop.

Was that with the StarWave 80ED ?

How is the Phenix 150mm, I had the 127mm f/9.4 and it was lovely for visual but shocking with a camera on board.

[laser_jock99]

Was that with the StarWave 80ED ?

 

How is the Phenix 150mm, I had the 127mm f/9.4 and it was lovely for visual but shocking with a camera on board.

I need to remove the Pheenix from sig- sold that a while back. The pic was with Starwave 80. I believe the newer version of this scope has improved correction.

[Purplehayze104]

nice pics can see wot you mean about the CA on the larger stars even after photoshop but mite give it a go one nite for giggles see wot comes out, whilst mostly been using the newt just be nice for a change

[laser_jock99]

The good thing about a Newtonian is that it's an apochromatic scope by nature!