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Do I Really Need Another Telescope?


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If you look at my signature below, you can see that I already have a SW 200P Dobsonian and a SW Evostar 120 achromat.  I also have a friend's 4.5 inch Meade reflector in storage, here in my spare room.

I've been dabbling with imaging with the SW Evostar 120, using a ZWO ASI224MC camera, with mixed results.  I've been recently trying to image the gas giants with some success, but as expected, I'm having to deal with chromatic aberration from the achromatic reflector.  I don't know if one of the Baader range of visual filters would help this situation or not.

I see that some people use their Dobsonians untracked, but I'm not sure if that would work for me (or even how to do it successfully).  I've been using my EQ5 GOTO mount for imaging, the only imaging I've done with the Dobsonian has been with a smartphone up at the eyepiece.

I've been toying with the idea of getting a SW 127 Mak and mounting it on the EQ5, for gas giant imaging.  I've also recently bought a 2x Barlow for increasing the size of the target in the camera frame, but obviously the Barlow cuts down the light entering the camera by a factor of four.

Should I look at buying a SW 127 Mak or are there other options (less expensive), that I've not thought about?🤔  Ideas are welcome...👍

Edited by Ian McCallum
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The answer to your question can be expressed by the formula n+1 where equals the number of telescopes you currently own.  So, 'Do I need another telescope?  n+1 then yes, yes I do!'

To answer your second query, a 127 Mak is a great scope to have in any collection.  I myself am currently looking for one to compliment my scopes.  I don't think you would be disappointed with one.

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1 hour ago, Ian McCallum said:

 

I've been toying with the idea of getting a SW 127 Mak and mounting it on the EQ5, for gas giant imaging.  I've also recently bought a 2x Barlow for increasing the size of the target in the camera frame, but obviously the Barlow cuts down the light entering the camera by a factor of four.

 

The Barlow does not affect in any way the number of photons from a planet which arrive at your camera. The light entering the front of your OTA has no idea whether or not there is a Barlow at the back of it so it is the same light. What the Barlow does is distribute it over a larger number of pixels, meaning each one receives proportionally less light in exchange for higher resolution. Since we can collect photons over time this matters very little in planetary imaging since the total exposure time is short anyway. A deep sky imager might feel differently since exposures are measured in hours.

Olly

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Another shout for the 127 Mak, I haven't put it on my EQ5, just on an Az GTi and it's excellent for lunar/planetary visual and photography. I bought the 127 Mak with the Az GTi as a kit, it's worth noting that if you buy the kit the dovetail bar is fixed so that can be problem in using the 127 in different orientations. 

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Completely anecdotally, but I’ve found that having a tracked set up can make up for an inch or two of aperture and not much more versus untracked. If you have good seeing that night, then even less (as you need fewer frames). 

Untracked is certainly more work and can be frustrating/difficult but that makes it far more rewarding. I would suggest trying out the dob a couple times to see if it’s not too annoying for you, because it will blow the 127mak out the water detail-wise. For me, it’s a matter of getting a well aligned finder and getting the planet drifting towards centre with an eyepiece before quickly swapping in the camera. Once it’s on the screen and the planet is drifting horizontally across the sensor then you just nudge each time it drifts out. 

Regarding the CA and filters, the baader fringe killer supposedly helps with that and I’ve seen people with the same scope reporting fantastic results. No personal experience though.

A perhaps more rogue suggestion is trying the 200p on the eq5. Normally a completely outlandish suggestion, but with your only aim being planetary keeping it in frame is sufficient and a good upgrade from untracked. The eq5 is rated for 9kg and the 200p OTA is 11kg so I’d check whether this is to the point where damage could occur, but if it’s just a matter of poor tracking then this could work. Far from ideal but as someone who images untracked with a dob this doesn’t seem so crazy for planetary!

 

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1 hour ago, ollypenrice said:

The Barlow does not affect in any way the number of photons from a planet which arrive at your camera. The light entering the front of your OTA has no idea whether or not there is a Barlow at the back of it so it is the same light. What the Barlow does is distribute it over a larger number of pixels, meaning each one receives proportionally less light in exchange for higher resolution. Since we can collect photons over time this matters very little in planetary imaging since the total exposure time is short anyway. A deep sky imager might feel differently since exposures are measured in hours.

Olly

I was going by the Inverse Square Law, as in you effectively double the focal length of the telescope and the light levels being received drop to a quarter of what the originally were.

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If you want to dabble with planetary imaging a little more (which is how I read your question) then I think I’d take @sorrimen’s advice and try the dob OTA on the EQ5- for the price of some tube rings and a dovetail- what could go wrong…

Or a more extravagant option may be to try the dob on a equatorial platform…

Both solutions would likely give better quality images for planetary targets than the mak 127 on an EQ5…
 

Although, I’d also agree with the other comments here that a 5 inch mak is a nice scope to have, but I just don’t think it’s the best option available to you for planetary imaging…

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I have, in the past used an EQ5 & 8" newt & DSLR for imaging. Straightforward motor drive. No guiding. No software stacking afterards.
With care you get a few minutes. But for short planetary work it should be easy. Especially with the 200mm diameter mirror.
You just need to look at the image size.
The benefit is that this doesn't cost you a new scope.

Equally the SW127 is a nice scope that is easy to store and use.

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58 minutes ago, Ian McCallum said:

I was going by the Inverse Square Law, as in you effectively double the focal length of the telescope and the light levels being received drop to a quarter of what the originally were.

Beware of the highly controversial F ratio myth.' Exposure time going as the square of the focal ratio is perfectly correct when you are altering the F ratio by altering the aperture, and the focal length remains constant.  When you do increase or reduce the F ratio by altering the aperture you do, obviously, increase or decrease the amount of incoming light. That's why the rule works.  But... when you alter the F ratio by using an extender or reducer at the back of the tube you have not altered the incoming light in any way. All you are doing with your rear element is putting the object photons onto fewer pixels (reducer) or more pixels (Barlow.) I think it's important to understand the difference in order to be able to decide whether a rear elemnt is worth it or not.

When you say, 'the light levels being received drop to a quarter of what the originally were,' it would be better say that they are reduced to a quarter per pixel but that they land on four times as many pixels.

Olly

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In your place, I'd try the cheapest option first - a filter for your frac. I recently read (it may well have been on here) a review of the three Baader filters which purport to combat CA. The Contrast Booster won over the Semi-Apo and Fringe Killer. I bought one, even though I have a dob, simply because it's also a good planetary filter. So if you bought the CB and it didn't reduce CA enough, you haven't really lost anything.

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1 hour ago, cajen2 said:

In your place, I'd try the cheapest option first - a filter for your frac. I recently read (it may well have been on here) a review of the three Baader filters which purport to combat CA. The Contrast Booster won over the Semi-Apo and Fringe Killer. I bought one, even though I have a dob, simply because it's also a good planetary filter. So if you bought the CB and it didn't reduce CA enough, you haven't really lost anything.

I've been using a Wratten #8, as a cheap man's CA filter.

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1 hour ago, cajen2 said:

In your place, I'd try the cheapest option first - a filter for your frac. I recently read (it may well have been on here) a review of the three Baader filters which purport to combat CA. The Contrast Booster won over the Semi-Apo and Fringe Killer. I bought one, even though I have a dob, simply because it's also a good planetary filter. So if you bought the CB and it didn't reduce CA enough, you haven't really lost anything.

I've gone and ordered the Baader Contrast Booster from @FLO, so I'll give that a try (weather permitting).

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5 hours ago, Ian McCallum said:

I've gone and ordered the Baader Contrast Booster from @FLO, so I'll give that a try (weather permitting).

 Can't do any harm and, who knows, it might just work. As a planetary filter, I've found darkening and colour change to be negligible on Jupiter and Saturn. There is just a subtle improvement in detail.I look forward to using it on Mars, where it's supposed to be excellent.

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Last night I was comparing (not for the first time) the Baader semi-APO with an unfiltered view, on Jupiter with my Skymax 127.

I bought the filter mainly for fringe-killing on my achromat, bbut with a possible secondary use as a planetary filter with any scope (it uses the neodymium substrate).

I've tried coloured filters on planets but didn't like them and found they removed detail, including the Wratten yellow. The semi-APO does give a yellow cast, but not too bad, and after a few seconds I got used to it. Did it improve the view? It was marginal, but at times I think that I could see just a little more.

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6 minutes ago, Zermelo said:

Last night I was comparing (not for the first time) the Baader semi-APO with an unfiltered view, on Jupiter with my Skymax 127.

I bought the filter mainly for fringe-killing on my achromat, bbut with a possible secondary use as a planetary filter with any scope (it uses the neodymium substrate).

I've tried coloured filters on planets but didn't like them and found they removed detail, including the Wratten yellow. The semi-APO does give a yellow cast, but not too bad, and after a few seconds I got used to it. Did it improve the view? It was marginal, but at times I think that I could see just a little more.

I don't have many filters, but I've never really tried coloured filters on the planets before.  I'm not a big fan of monkeying around with various filters, during a session.  I prefer either to stick to the one or none at all.  Having said that, I do like to try a neutral density moon filter, with and without on the lunar disk.

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Given that planetary imaging benefits from aperture to maximise the resolution, I reckon sticking the 200p on an EQ platform would be well worth trying. They are pretty simple to set up, and will track for 45 mins or so, plenty long enough for imaging captures which would only be a few mins.

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2 hours ago, TheThing said:

This thread made me buy a SW 127 mak.  Nothing else, just this thread. 

Cant wait to pick it up now.

I don't think you'll be disappointed.

I bought mine second hand from an SGL member and I use it most of the time now. It really is very capable for the size and cost.

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Another plus vote for the 127 Mak. I have both the Mak and an 8” SL dobsonian. Both are extremely capable planetary scopes. I also have a 120/1000 Evostar with a 2” semi apo filter permanently in the diagonal. This also fares relatively well on the planets. For resolution the dobsonian wins out and for contrast my 102 apo refractor wins out.

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5 hours ago, Zermelo said:

Did it improve the view? It was marginal, but at times I think that I could see just a little more.

I've tried the Neodymium, Semi-Apo and Contrast Booster filters from Baader, and I thought the Contrast Booster had the most effect out of the three. The Semi-Apo seems like a weaker Contrast Booster and the Neodymium's effect was even subtler. This was using them all as "planetary contrast enhancement filters" rather than just a minus violet and my scopes are ED refractors.

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11 hours ago, Stu said:

Given that planetary imaging benefits from aperture to maximise the resolution, I reckon sticking the 200p on an EQ platform would be well worth trying. They are pretty simple to set up, and will track for 45 mins or so, plenty long enough for imaging captures which would only be a few mins.

Would my SW Skyliner 200P not be too much weight for the EQ5 GOTO mount?  The OTA alone weight in at 11kg.

Edited by Ian McCallum
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3 hours ago, Ian McCallum said:

Hence my question.😉

Some folk load their mounts right up to the max and there's nothing wrong with that as it won't break the mount or anything, but I find I get better performance when I don't give my mounts a hard time. Focusing at higher powers can be frustrating when the scope vibrates a lot and the slightest breeze causes your view to dance around. I try and follow the advice given by astro-imagers and don't go above 3/4 of mount capacity or even 1/2.

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