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Birthday coming up


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Birthday is always a good excuse to treat yourself to some new gear, right?

I've had my eyes on a Newton and a 150/750 for AP which seems like a good balance for me. Talking to the owner of astro-art he recommended the Lacerta coma corrector, as I understand it it's a GPU-design? However I'm not quite sure what that means. The alternative would be the somewhat cheaper Baader MPCC Mark III. What are the differences here?

I've also thought about the guiding requirements. I'm currently getting around 0.8" - 1.4" and I feel like I would need to improve that as my pixel resolution is going from about 2.2" to 1.3". Am I right in that my guiding error should not greatly exceed my pixel resolution? The options I've seen here is:

  1. Upgrade my guide scope to a better quality and maybe higher focal length.
  2. Get an off-axis guider.
  3. Use my Z73 on top of the newton as a guider.

I mostly feel like option 2 and 3 are the most interesting. There's also the possibility that my mount is simply too worn and needs an upgrade or replacement.

Otherwise, going from a refractor to reflector I'm thinking I'll have to manage collimation so I know some thumbscrews for the secondary is always encouraged. I have a laser collimator which I'll see if it works for me.

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2 hours ago, Shimonu said:

What are the differences here?

The GPU is certainly a better corrector than the MPCC but at F5 the Baader should be ok. There are always plenty going second hand on Astro Buy And Sell so you could try it and resell if you aren't happy. I have both and the GPU is better on my F4 but at F5 there is not much in it. The GPU is quite fussy on distance to the sensor.

WRT the guiding, the scope you have have should be fine to guide the 750 FL. If you are not getting good enough results look at the mount. Both my SW mounts needed fettling before they were acceptable. They do suffer from backlash when not fully 'tuned'. You could go down the OAG route but at 750mm you don't need to.

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14 minutes ago, Clarkey said:

The GPU is certainly a better corrector than the MPCC but at F5 the Baader should be ok. There are always plenty going second hand on Astro Buy And Sell so you could try it and resell if you aren't happy. I have both and the GPU is better on my F4 but at F5 there is not much in it. The GPU is quite fussy on distance to the sensor.

WRT the guiding, the scope you have have should be fine to guide the 750 FL. If you are not getting good enough results look at the mount. Both my SW mounts needed fettling before they were acceptable. They do suffer from backlash when not fully 'tuned'. You could go down the OAG route but at 750mm you don't need to.

Much appreciated. When you say the GPU is fussy, you mean even caliper measurements won't give you any guarantees, I'd likely need to fine tune it?

Currently I'm looking at the TS Optics 6" f5. I see you have the f4, did you ever consider the f5? As far as framing goes it doesn't seem like you miss out on any targets. My thinking for the f5 was that the collimation would be easier. As it's my first newton I figured it would be a gentler introduction for me.

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9 hours ago, Shimonu said:

When you say the GPU is fussy, you mean even caliper measurements won't give you any guarantees

You might be Ok with calipers, but I used the standard 55mm spacers and I needed to add another 0.25mm. I purchased some of the Baader delrin spacers which worked fine. The GPU also needs pretty perfect alignment with no tilt. Obviously I am doing this for an f4 scope - at f5 it might be less fussy.

 

9 hours ago, Shimonu said:

Currently I'm looking at the TS Optics 6" f5. I see you have the f4, did you ever consider the f5?

Yes, but I wanted an optically fast scope to 'replace' the ED80 but with a similar FL. The ED80 with reducer was F6.3 with a FL of 510mm. I would have actually preferred even shorter, but it does not exist within my budget. One thing to consider about the TS scopes is the poor focuser. The monorail is poor and either slips or 'rebounds' with small changes. I changed it for a Baader Steeltrack which was a bit of a faff as the OTA is really too small. Other people have made similar comments. Personally, if you are happy with F5 I would consider the SW 150 PDS as the stock focuser is better.

You are right about collimation. F5 is easier than F4. However, as I have managed ok with F5 and collimated an RC8 too, I felt it would not be too much of a challenge. Also, I have a cupboard full of collimation aids. For the standard F5 a Cheshire should be fine. 

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