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Disappointing view with new 'scope


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Hello everybody, having gleaned a lot of info from the forum over the last year, many thanks by the way, I finally took the plunge and replaced my Helios 150mm refractor with a SharpStar 94EDPH f/5.5 Triplet Apo.

I intend to use it firstly for visual observation, with the option for imaging later when funds permit.

The lenses I already have are Explore scientific 70 series, 20mm and 10mm, and a 52 series 4.5mm.

I have a stella mira 99% dialectric diagonal.

So I set it all up, very excited to see this high contrast sharp image, inky black sky and sharp stars and planets. No such luck.

Venus and Jupiter both had fringes. Red on one side, blue on the other. Venus was particularly bad, the fringes being as large as the size of the planet.

The moon looked reasonably OK with the 20mm lens, but poor contrast with the other two lenses. Certainly not that feeling of being able to step out onto it.

I know the seeing has been less than ideal, but I am struggling to see any improvement over what I had before.

There must be a weak link somewhere. Could someone point me in the right direction to find out what it is please?

Sorry to start my first post with a problem.

many thanks

Mark

 

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6 minutes ago, Mark99 said:

Venus and Jupiter both had fringes. Red on one side, blue on the other

My Tak did this a while back due to atmospheric dispersion due to Jupiters low altitude and really poor conditions. This scope has superb optics and a perfect star test that I mention because outside influences can detract from any scope.

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@Mark99 did you leave the scope to cool for a while? Triplets can take a good while to get acclimatised.

As Gerry said, atmospheric dispersion causes red and blue colour shift looking much like scope CA but easily identified.  How high was Jupiter when you observed it?

Conditions are all for planetary observing. If it makes you feel better, I’ve recently got an LZOS 130mm f6 and have yet to have any planetary views that make me go ‘Wow’! I’ve seen some periods where I think ‘ooh yes, that’s nice’, but I know there is a lot more to come when the skies are at their best, it’s just a waiting game really.

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Thanks for the encouraging replies. I'm hoping with the cold front having just come through here, that there will be some spells of clear air tonight that should give some better seeing. I'll get the gear ready early to allow it to settle down nicely first

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Agreed with what have been said above. Also have you tried with straight-thru view? This is just to eliminate the diagonal from the optical path in case it's broken. And f/5.5 is pretty fast, probably too fast for your ES70 eyepieces.

Jupiter isn't at its best altitude yet, but with sufficient cooldown and observing near the meridian under above average seeing there shouldn't be any visible CA in a well collimated triplet. That's what I saw with my APM 107 last week which is also a sharpstar scope.

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11 minutes ago, MillHey Nebula said:

How do you distinguish between CA and atmospheric dispersion?

With 'AD' you will have a red fringe on the side towards the horizon and a blue fringe of the other (when planet is centred in view).

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1 hour ago, Mark99 said:

Venus and Jupiter both had fringes. Red on one side, blue on the other. Venus was particularly bad, the fringes being as large as the size of the planet.

Are you saying red/blue fringes on either side of best focus or more like AD above when in focus?  It's not unusual for APOs to have red or blue fringing on either side of best focus.  It's the nature of the beast.

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Supposedly, the prisms in the ADC units correct the entire field.  I would think the software method would work the same way.  There is some variability of AD from top to bottom in wide field shots (more than a couple of degrees), so software would have to accommodate them for best results.  However, AD may not be visible in truly wide angle images.

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Thanks so much guys, looks like AD then.

I can't bring the 'scope to focus straight through. I do need to check the diagonal as that is a new (secondhand) acquisition.

KP, can you give me some pointers on the type of lenses I should be looking for?

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3 hours ago, Mark99 said:

Thanks so much guys, looks like AD then.

I can't bring the 'scope to focus straight through. I do need to check the diagonal as that is a new (secondhand) acquisition.

KP, can you give me some pointers on the type of lenses I should be looking for?

These imaging oriented fracs require extension tubes to reach focus without a diagonal.

Your ES70s afaik are pretty much the same as many other 70 afov eyepieces based on the 5-element Erfle design. (e.g. WO SWAN). These kind of eyepieces aren't going to give you the best views with scopes faster than f/6. If you're on a tight budget and ok to sacrifice a bit of fov, BST starguiders are worth a look. They are supposed to be good down to f/5. More expensive options include ES68, ES82, Baader Morpheus and APM UFF (Altair also sell the same range under their own name). Or for top of the line ES92/100, Televue, Pentax XW or Nikon NAV.

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7 hours ago, Mark99 said:

Thanks so much guys, looks like AD then.

I can't bring the 'scope to focus straight through. I do need to check the diagonal as that is a new (secondhand) acquisition.

KP, can you give me some pointers on the type of lenses I should be looking for?

I have the same diagonal (assuming it's the 1.25" version) and it's got a relatively long optical path compared to the prism I'm currently using with my new scope. I haven't been able to find the figure for the optical length of that particular model, but a similar looking one from Astro-Tech apparently has a 94mm path length.

What that means is that without the diagonal in place and with the focuser at the same position, you would need to add 94mm of extension to allow your existing eyepieces to reach focus.

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Congratulations on a fine scope!

Be patient my friend, some nights under certain conditions I too see blue and red color fringing on either side of Jupiter and bright stars, then the next night it’s gone. This happens, there are many variables, I’m using a TSA-102, if it happens to me it will happen to anyone 😂😂😂 no I’m not bragging, just reassuring you your scope is fine.

Give it time, every one of us when using a new scope becomes super sensitive about what they see and the slightest unexpected phenomenon can send chills down our spines. 

Edited by Sunshine
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Thanks for all the useful info, plenty to take on board!

Found an extension tube that I didn't know I had, (can't remember why I bought it) so I will be able to test the straight through view.

I suspect I was super sensitive using the new scope for the first time. It had had a big build up!

I think I will hold off on eyepieces until I can get some to match the quality of the scope. One at a time would be a plan. More stuff to research endlessly on the internet. We love research don't we?!

 

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Make sure to give that triplet plenty of time to acclimate.  I have to allow 30+ minutes for my 90mm triplet to equilibrate before the spikes around stars settle down.  The first time I looked through it, I freaked out thinking it had pinched optics.  It just needed time outside to settle down.

Edited by Louis D
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7 hours ago, Mark99 said:

Thanks for all the useful info, plenty to take on board!

Found an extension tube that I didn't know I had, (can't remember why I bought it) so I will be able to test the straight through view.

I suspect I was super sensitive using the new scope for the first time. It had had a big build up!

I think I will hold off on eyepieces until I can get some to match the quality of the scope. One at a time would be a plan. More stuff to research endlessly on the internet. We love research don't we?!

 

As others mention cool down is very important - best to remove the diagonal and eyepiece in the back of the scope and then point the front of the scope 45’ down so warm air can escape for at least 30 mins.

Once cooled find a bright star that is very high - there are a couple in the southern sky at the moment and look at those both in and out of focus.

You should see no colour at perfect focus and possibly a red and blue tint on opposite sides of focus. As long as you see no colour at focus you are fine.

 

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