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Old 06-03-2019, 09:53 PM
Astronovice (Calvin)
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Astronovice is offline
 
Join Date: Jun 2017
Location: Cairns Northern Beaches
Posts: 81
Quote:
Originally Posted by gregbradley View Post
There is a bit of a scale of quality with refractors.

Here are some known good companies:

1. Teleskop Services. They have a broad range of scopes. A number of these are clones that are simply wearing their brand and you'll see the same scope elsewhere rebadged. But it seems like occasionally they demand a bit more from the same scope which is good.

2. Stellarvue. They have a good name. Their prices are probably a bit higher but you are less likely to have issues.

3. William Optics. They can sometimes be good. Check reviews though as I do read of the occasional dud.

4. Esprit. It seems these are quite high end triplets.

5. Astrotech - they often rebrand these same scopes as Teleskop Services, Skywatcher and others.


As a general rule triplets are better corrected for false colour than doublets although I see a lot of FPL53 (premium ED glass) and Lanthanum doublet scopes these days. How they perform is a bit hard to tell but from sample images some brands post they perform quite well.

Also keep in mind that the Q style refractors are more suitable for imaging than the straight triplets etc. Teleskop services lists their Q type astrograph refractors separately. They are often around F5 which is nice and fast and they should have more perfect stars in the corners.

As I understand it, a lot of these FPL53 triplets are lenses made by Canon iOptron and then they are fitted into various telescope bodies so the standard seems to be quite high.

APO refractors used to be extremely expensive and in the last several years they have come down a lot in price and the quality has risen.

To complete the list the high end scopes are:

1. Takahashi.
2. AstroPhysics.
3. TEC (Telescope Engineer Company).
4. APM.
5. CFF.

Astrophysics have a wait list so not that practical to list them but their scopes often come up in 2nd hand marts.

CFF would be my current top notch choice or Takahashi. APM used to be super high end but their strehl ratios are lower than Takahashi, CFF.
TEC are very good but optimised for visual so a bit weak in the red channel.

When considering a refractor I would;

1. Consider the brand as above.
2. Triplet is usually better than a doublet.
3. FPL53 is the premium glass and usually only 1 element is FPL53 and then the other 2 elements are some lesser glass. That is normal. If it were FPL51 I would be less interested.
4. Focuser. A good focuser is a must. It needs a micro adjuster as well.
Larger focusers are better than shorter ones.
5. How wide is the corrected circle of the scope? That means the circle where all the stars are round and not distorted.
6. Accessories - guide scopes, mounting rings, flatteners and reducers (a flattener makes stars round in the corners, a reducer makes the F ratio lower and the field of view wider making for faster imaging and wider views).

I hope that helps.

Greg.
Thank you Greg,

Your comments are most helpful.

Am I right in assuming that Hoya FCD100 and Ohara FPL53 are broadly equivalent?

Calvin

Last edited by Astronovice; 06-03-2019 at 11:00 PM.
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