13 replies to this topic

[damarks913]

Can someone please let me know opinions and major differences between these small refractors, or any other similar suggestions for wide field scopes?

 

https://www.astrosho...-v2-ota/p,62741 (reducer/flattener another ~$200)

 

https://www.astrosho...red-ota/p,56055 (~$230 for reducer/flattener)

 

https://www.astrosho...dph-ota/p,63320 (reducer/flattener included)

 

Thank you

[bobzeq25]

Opinion.

 

They're all excellent choices for learning DSO astrophotography.  For that, your choice is not critical.

 

The more expensive one will have better optics and focusers.  This marketplace is pretty efficient.

[the Elf]

Hey,

 

#1: AP 61/274 EDPH is an FPL53 triplet, the lens with the best color correction

#2: AP 60/360 PhotoLine is an FPL53/lanthan doublet. The color correction is very good but not as good as the above

#3: AP 70/420 ED is a doublet as well but the glass is not specified, that means it is the worst of the three

 

#1 is missing a rotator, the other two have one. If you want a threaded connection to the camera you probably want a rotator. The sell one for about $100 if you want to add it to #1.

They differ in focal length, obviously. How large an object fits the FOV depends on the sensor size. When you go for a longer focal length larger objects may not fit the FOV, if you go for shorter small objects do not show much detail. You have to make a decision what you want to do. In general a shorter focal length is easier to handle and less demanding on your mount.

#1 is know for a too short dovetail. If you want to balance it with the camera attached you have to buy a longer dovetail. f/4.5 on the one side is fast, collecting a lot of light, the downside is you have to focus very precisely. A slightly slower scope is a bit easier to focus.

#2 and #3 are missing a dovetail, so in any case you need to buy one. I don't know if they fit a tracker.

#1 is the only one with a decent mounting option for a guide scope.

 

Similar/better:

https://www.teleskop...3-Objektiv.html

A FPL53 triplet, flattener in the scope, rotator, a long dovetail and two rings, guide scope can be mounted on top, 3'' draw tube

 

The scope is only the second most important selection. Far more important is which mount you have/want to buy or if you want to use a tracker. If you have a feeling this is going to be a long time hobby you should start with a big solid mount. Over the years you will add telescopes because there is no one fit's all. On the other hand if you need something portable, e.g. to take on a hiking tour it is a different story.

[F.Meiresonne]

Hey,

 

#1: AP 61/274 EDPH is an FPL53 triplet, the lens with the best color correction

#2: AP 60/360 PhotoLine is an FPL53/lanthan doublet. The color correction is very good but not as good as the above

#3: AP 70/420 ED is a doublet as well but the glass is not specified, that means it is the worst of the three

 

 

Attention,

 

#1 is the older 61 EDPH doublet(also stated in the specs), this is not the 61 EDPH mark II which is a triplet....indeed.

Also the price is way too high , i bought mine in the UK, the doublet version

 

This is the Mark II triplet now also available with TS

https://www.teleskop...ture-F-4-5.html

 

Confusing i know,

 

I have both the Sharpstars 61 mm and the 76 mm so i am familiar with  them...TS sells them  under private label...

The 76 mm i bought with TS, great scope..

Edited by F.Meiresonne, 19 January 2021 - 03:50 PM.

[damarks913]

thank you all. What I am finding is there is a lot of 3 card monty with the same scope or very close under different brand names.

[the Elf]

Freddy, thank you for correcting this. To me the images on the astroshop page and the TS page looked identical. A price of 880€ must be a triplet or it is way too high.

 

Anyway, to the OP:

question to put for a scope decision:

- Which field of view?

- Which optical quality in terms of color correction (FPL53 triplet - FPL53/lanthan doublet - "special glass" ED doublet - Fraunhofer doublet ) in that order from high to low

- a flat field design with flattener in the scope or an external flattener or flattening reducer?

- do you want to use it for observing as well (not recommended)?

- for threaded camera connection: is a rotator included? (not relevant for slip in)

- two rings and long dovetail vs. less stable single ring brackets?

- length of dovetail to balance the setup

- R+P focuser vs. Crawford

- where/how to mount the guide scope? (Do NOT use the finder shoe.)

- which f-ratio with respect to sensitivity to temperature change and sensitivity to exact focus

- length, weight, mount capacity

- finally: budget

 

The hidden cost items are: need a longer dovetail, need an extra bar to mount the guide scope, need for a separate rotator, poor focuser that needs update, flattener/reducer and dew straps. This can easily add several 100 $/€ or even exceed the scopes price!

[the Elf]

My latest pitfall:

I ordered this scope for visual:

https://www.teleskop...-P-focuser.html

The rotator is missing, so I ordered this:

https://www.teleskop...M54-und-2-.html

 

The dovetail it mounted to very thing rings, see detail photos on the TS description. The two screws are just one single turn in the thread, for to little for a save connection. So I had to upgrade to this bar in order to use the two longer/deeper threads of the rings.

https://www.teleskop...pport-area.html

The resulting distance of the rings meant I could not use the original dovetail for my telrad, that I want to use on all my telescopes and I had to order this as well:

https://www.teleskop...long-bores.html

 

I refuse adding up the figures. I just don't want to know. The point that really makes me angry is that they know the connection is not save. There is a more expensive scope using the same rings but with a bar that is connected to the longer holes. As I said before: I am not exactly a fan of TS but they have something close to a monopoly in Germany.

[copper280z]

I've got the v1 61edph (doublet). It's a great scope, color isn't perfect, but it's really really good. It holds focus well, the field is flat and well illuminated on APS-C, and the optical quality outside of color correction is as near flawless as I can detect.

Overall it's been incredibly easy to use and worked as expected, I'd recommend it for sure, but not for $1k. Sharpstar is the manufacturer, and you can find that brand name a bit cheaper.

[F.Meiresonne]

Can't see much color indeed in 61EDPH doublet.

 

I posted an image here on CN once from a jpg. I always record a . CR2 file and dito .jpg. It was of the M35 cluster...no trace of color on that jpg around any star.

But i can't seem to find it anymore.

 

I am pleased with my 2 Sharpstars. One advantage, they come if desired with a dedicated FF/FR, easy to screw in and no hassle with the distance...

[the Elf]

Here is an example what an FPL53 triplet delivers. Watch it zoomed in to 100% and check the corners. Not a trace of a color fringe, perfect round stars, plenty of dim single pixel stars. It is the perfectionist's choice.

https://www.elf-of-l...s_2019_full.jpg

The noise comes from lack of data or stretching it too much.

 

Please note: a "new" glass is around since a few years called FPL55. Now the first telescopes featuring this sort is available. It seems to be optically very close to FPL53 but cheaper and easier to grind. A too good to be true story as it seems. Just in case one crosses your path.

[copper280z]

I'll offer this as evidence of what a good doublet delivers, it's just slightly cropped from full APS-C size to exclude stacking artifacts.

 

[F.Meiresonne]

This is a enlarged picture of a star on a jpg straight from the camera, not stacked

 

61 EDPH doublet

Attached Thumbnails

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[the Elf]

Here is a 100% crop of copper280z's doublet and my triplet half way between the center and a corner. As you can see the difference is visible on pixel level only. If you have only one scope and want to image objects much smaller than the field of view this might concern you. When the object is large and the image is presented less zoomed in you cannot really see a difference. The minimal color fringes make either red or blue stars look more intense in color. This can be corrected reducing saturation if it is too much. As I say, the triplet is for perfectionists but a FPL53 doublet is still a very good performer. When your budget is limited it might be a good choice to go for the cheaper doublet and invest the saved money in a better mount. If the mount does not track well and elongates the stars either scope cannot deliver a good image. The weakest link story.

 

Edited by the Elf, 21 January 2021 - 04:13 AM.

[copper280z]

Here is a 100% crop of copper280z's doublet and my triplet half way between the center and a corner. As you can see the difference is visible on pixel level only. If you have only one scope and want to image objects much smaller than the field of view this might concern you. When the object is large and the image is presented less zoomed in you cannot really see a difference. The minimal color fringes make either red or blue stars look more intense in color. This can be corrected reducing saturation if it is too much. As I say, the triplet is for perfectionists but a FPL53 doublet is still a very good performer. When your budget is limited it might be a good choice to go for the cheaper doublet and invest the saved money in a better mount. If the mount does not track well and elongates the stars either scope cannot deliver a good image. The weakest link story.

compare.gif

That's a really cool demonstration!