Recommend me a refractor

[swannies1983 (Dan)]

How many types of ED80s are there? Which one do people recommend?

[Hagar (Doug)]

Originally Posted by swannies1983

How many types of ED80s are there? Which one do people recommend?

Dan, There are an awful lot of brand names out there but you will find most come out of the same factory in China (Synta).
I have not had anything to do with the 100mm version but can recommend either the 80mm or the 120mm refractors from this factory. (Orion, Skywatcher and astrotech) are just a few of the brands from Synta.

Which ever you choose you will need a field flattener but these are readily available.

If you have an 8" Newtonian you will search hard for a nicer imaging scope. Using a Comma corrector to fix the comma and an upgraded focuser will give you an excelent imaging scope with some money left over to celebrate your images with.

Good luck with your search.

[g__day (Matthew)]

Given that Bintel sell Meade OAG for $109 https://www.bintelshop.com.au/Product.aspx?ID=5443 it wouldn't be dear or difficult to try prime length guiding. If you could sell the Tasco could could probably come out almost even.

Full focal lenght guiding will show the ability of your guiding skills and your mount's capabilities; and consequentially be alot cheaper than a new OTA. For long exposures if you don't go OAG - then you'll need very rigid gear to guide well (to eliminate or at least minimise differential flexure). I spent over a grand on my mounting gear and same again on focusers that can be PC controlled.

If your intended targets are dim they will require long duration guiding. For this to be successful you need really, really sturdy amd rigid gear - throughout your entire imaging chain, and possibly a way to maintain precise focus as the night progresses and therefore cools and this changes your OTAs focus.

[swannies1983 (Dan)]

Originally Posted by g__day

Given that Bintel sell Meade OAG for $109 https://www.bintelshop.com.au/Product.aspx?ID=5443 it wouldn't be dear or difficult to try prime length guiding. If you could sell the Tasco could could probably come out almost even.

Full focal lenght guiding will show the ability of your guiding skills and your mount's capabilities; and consequentially be alot cheaper than a new OTA. For long exposures if you don't go OAG - then you'll need very rigid gear to guide well (to eliminate or at least minimise differential flexure). I spent over a grand on my mounting gear and same again on focusers that can be PC controlled.

If your intended targets are dim they will require long duration guiding. For this to be successful you need really, really sturdy amd rigid gear - throughout your entire imaging chain, and possibly a way to maintain precise focus as the night progresses and therefore cools and this changes your OTAs focus.

Would I need a coma corrector when using an OAG given I will be trying to find stars at the edge of the field? How does the addition of the OAG impact upon the point of focus? I was lucky in that I didn't have to cut my tube and change the position of the primary mirror as I could attach my DLSR directly to the thread where the 1.25" adapter plate is. I only have about 5mm of inwards focus remaining. What does the OAG do to the setup?

[Alchemy (Clive)]

Originally Posted by swannies1983

How many types of ED80s are there? Which one do people recommend?

I had the gold tubed one, surprisingly good optics, although ED it really is APO the focuser worked fine no problems that I picked. It then became a guidescope, and as I wanted a faster guidescope I replaced it with a Williams megrez 88 f5.6 I sold the ed80 to another IIS member.... One who has replied to this thread and also recommended an ed80.

Would have to be the best bang for your buck around IMO.

[RobF (Rob)]

It's unlikely the 60mm guidescope wouldn't be at least as good as a finder guider Dan. Could I ask what sort of imaging you lust after? What sort of objects (big nebs or smaller galaxies) and what sort of camera and sub length is the goal? Do you have a fixed set up?

I guess what I'm thinking without knowing more is that if you're setting up and pulling down all the time much of the frustration that has prevented you setting up in the last 1.5 yrs (polar alignment, etc?) may still be a significant issue in a refractor setup.

[swannies1983 (Dan)]

Originally Posted by RobF

Could I ask what sort of imaging you lust after? What sort of objects (big nebs or smaller galaxies)

It's probably a combination of both. I understand that the refractors within my price range would be better suited for wide view imaging, which will probably be a good starting point. I still have my newt for smaller objects.

Originally Posted by RobF

and what sort of camera and sub length is the goal?

Unmodded Canon 400D. I would probably like to get out to 5 mins. I can get out to this length with some room to play with before skyglow becomes a problem. However, the plan is to eventually get a light pollution filter though.

Originally Posted by RobF

Do you have a fixed set up?

No I don't.

Originally Posted by RobF

I guess what I'm thinking without knowing more is that if you're setting up and pulling down all the time much of the frustration that has prevented you setting up in the last 1.5 yrs (polar alignment, etc?) may still be a significant issue in a refractor setup.

haha, the main reason why I haven't gone out in the last 1.5 years is because the wife and I had a baby

But yes, I was getting a bit frustrated setting up the newt each time and trying to get the correct balance. I was thinking a smaller scope would produce less problems, but maybe this isn't always the case.

[alistairsam]

Hi,
any thoughts from anyone on the long perng scopes at andrews.
I've not seen or tried them but they do seem to have good build quality.

I've been thinking about one of these.
http://www.andrewscom.com.au/site-co...-longperng.htm

Achromatic 80mm f/6 OTA doublet refractor
$349.00 AUD

CARBON FIBRE ED 80mm DOUBLET
ED APO 80mm f/6.25 carbon fibre refractor with ED fluorite lens and Series 2 Crayford style 2" 4 kg. capacity 11:1 microfocuser!
$599.00 AUD

ED APO 80mm f/6.8 OTA
$499.00 AUD
Includes FPL-51 fluorite ED lens


if you use a filter wheel with LRGB filters, a monochrome camera, would a doublet be good, as then you could get a bigger aperture for a lower price than the apo's and you wouldnt have chromatic aberration as you're shooting in monochrome?
is this correct? there's bound to be a catch somewhere with this?

Edit: Dan, I just noticed you're planning on using a 400D. but just wanted to ask the monochrome question nevertheless.

[Hagar (Doug)]

Originally Posted by alistairsam

Hi,
any thoughts from anyone on the long perng scopes at andrews.
I've not seen or tried them but they do seem to have good build quality.

I've been thinking about one of these.
http://www.andrewscom.com.au/site-co...-longperng.htm

Achromatic 80mm f/6 OTA doublet refractor
$349.00 AUD

CARBON FIBRE ED 80mm DOUBLET
ED APO 80mm f/6.25 carbon fibre refractor with ED fluorite lens and Series 2 Crayford style 2" 4 kg. capacity 11:1 microfocuser!
$599.00 AUD

ED APO 80mm f/6.8 OTA
$499.00 AUD
Includes FPL-51 fluorite ED lens


if you use a filter wheel with LRGB filters, a monochrome camera, would a doublet be good, as then you could get a bigger aperture for a lower price than the apo's and you wouldnt have chromatic aberration as you're shooting in monochrome?
is this correct? there's bound to be a catch somewhere with this?

Edit: Dan, I just noticed you're planning on using a 400D. but just wanted to ask the monochrome question nevertheless.

Hi Alistair, Your question is quite a complicated one but the reality is that the use of an achromat and a mono camera should render the chromatic aberation null and void but would require a refocus with each and every change of the filters. This is at least in theory.
The ED scopes using either FPL-51 or FPL-53 glass, even in the doublet lens arrangement would correct most if not all the aberations on all but the very brightest of objects. Some aberations may exist on things like a full moon but even then much much less than the achromat.
The cost difference is well worth the quality you find in such lens systems.
The use of ED refractors is a massive step up to the achromat and is considered an APO or semi APO refractor. It';s use will also return good filters to par focal or at least very very close to this.

[g__day (Matthew)]

Programs like PHD can do a centroid find on a soft or coma affected star quite well. Back focus may be an issue - if the OAG is 30mm wide say - its has to be accounted for in your reaching accurate focus.

Its most common to see OAG used on long focal length tubes - like SCT which also have a serious lot of back focus available from their inate design of moveable primary mirror.

[gregbradley]

Achromats are no good for imaging and you will get blue halos around stars.

I am not 100% sure refocusing on each filter will stop the blue halos. I think not because you will probably get bloated stars in the blue subexposures but not 100% certain of this point.

Even so who wants to have to refocus for blue. A lot of extra work without automation software which will do it but it now requires an autofocuser software program and just another thing to bug up at 2am.

My scopes have the same focus for each filter. I checked.

Triplets outperform doublets generally. But the ED80 with the FPL53 (not FPL51) is the one that is used a lot and gives great results.

I read a thread about carbon fibre for refractors and Roland Christen seemed to be against it. Tube currents. Also aluminium tubes shrink with temperature but tends to match the shift in the lens with falling temps to some degree. Not conclusive. I wonder if those who are using a carbon fibre tubed APO can comment about tube currents and focus shift with temp changes?

ED80 is also super light which means it is easier for the mount to get better tracking results.

Greg.

[alistairsam]

Originally Posted by gregbradley

Achromats are no good for imaging and you will get blue halos around stars.

I am not 100% sure refocusing on each filter will stop the blue halos. I think not because you will probably get bloated stars in the blue subexposures but not 100% certain of this point.


Greg.

As there are two types of chromatic aberrations - axial and lateral, that is different focal points along the optical axis and the other with different focal points on the same focal plane, I'm guessing achromats might result in lateral CA, so no need to refocus but there might be a slight lateral image shift with different wavelengths. So I wonder if re-positioning the blue images would correct the blue halo.

As all have mentioned, the semi-Apo's or ED series would be a good investment and a 102mm ED would be ideal.
The Black Diamond 102mm ED is 1199 at Andrews.

I'm going to try the Long perng ED's.
The ED APO 80mm f/6.8 OTA which Includes FPL-51 fluorite ED lens at $499.00 AUD is within my reach.
but a bit confusing because the description mentions this is a doublet which is two lenses, but also says its an Apochromat which is 3 lenses. might have to check with them.
Or the ED APO 80mm f/6.25 carbon fibre refractor with fluorite FPL53 ED lens at $599.00 AUD

Let us know what you end up choosing Dan.
A light portable AP setup is enviable.

[swannies1983 (Dan)]

It all comes done to funds and whether I sell my Tal. I have been following a thread on another site where they have been discussing changing the standard 1.25" focuser to a 2" one. It's not that easy and depends on the focuser that is used. Inwards focus is the problem as the baffle tube, just below where the focuser sits, is narrower then the 2" focuser drawtube meaning there's a limit as to how much the focuser can travel inwards. Bert's image train is another option but hopefully this alternative works.

Going by what's in this thread, I think the ED80 would be the best option. The lower price will allow for me to have some spare cash for a flattener. This will probably be my choice if I want a wide view imaging option.

[gregbradley]

The term APO has been hijacked in marketing hype to mean any scope with decent colour correction. It actually has a definition of 3 colours at the same focal point. Usually in practice that means a triplet but if it can be done with a doublet then it would meet the definition. Usually they don't but there are high quality doublets. The Tak FS series for example.

Orion ED may not be APO by definition but perhap best described as high end semi-APO. Tak FS series also.

If you can get a triplet for the same money you should be better off.

Fluorite is another marketing hype. Fluorite is a crystal not a glass. FPL53 has fluorite in it so marketing uses the favorable term fluorite to make it sound more marketable. Real fluorite is more expensive. TEC are one of the few scope makers who still do fluorite lenses. Officina Stellare are another.

Greg.

The ED APO 80mm f/6.8 OTA which Includes FPL-51 fluorite ED lens at $499.00 AUD is within my reach.
but a bit confusing because the description mentions this is a doublet which is two lenses, but also says its an Apochromat which is 3 lenses. might have to check with them.
Or the ED APO 80mm f/6.25 carbon fibre refractor with fluorite FPL53 ED lens at $599.00 AUD