Ricochet

I've just used some white electrical tape on the outside and flocking the inside has covered the holes on the inside.

No cheaper alternatives as far as I am aware. There wasn't even a Clicklock on the market when I ordered mine. I had to get calipers out and measure the threads on the focuser, and being a prototype, it cost maybe double what you would pay for for the production version. (Mine is actually an M68/1 Clicklock with an M68/1 to M68/0.75 converter ring, I don't know if the production model is the same of M68/0.75 on all threads.)

Wrapping the tube to keep the inside temperature stable works with Maks/SCTs because they are closed systems and there is no/little air movement if the air is stable. With a Newtonian the fact that it is open at both ends means you are still going to get convective currents rising up the tube if the air inside the scope is warmer than that outside. Where you might see an improvement is in the situation detailed at the linked website where dew formation causes cools the metal tube and this cools the air inside below the ambient temperature. I have flocked the inside of my OTA, which is a plastic sheet with a fibre surface, and I suspect that this might actually insulate the air inside the tube from the tube itself in a manner like you are suggesting. Dew formation on my scope seems to be limited to the outside of the OTA, whilst the inside remains dry and relatively warm to the touch (not that I have made a habit of touching the inside of my OTA).

The focuser on the 76p is a standard rack and pinion focuser, nothing like the threaded helical focuser on the 130p/150p. You might find that the PTFE tape is quickly compressed out of position when winding the focuser in and out. The usual method of improving the play in a focuser like yours would be to increase the thickness of the shims on the inside of the focuser that push against the draw tube. See the following thread:

Yes, the click lock is excellent, whilst the standard Hexafoc 2" clamp is absolute garbage as it is too shallow. From memory it is something like 2mm of metal, and 8mm clamping ring and then another 2mm of metal. Any sort of undercut on an eyepiece or 1.25"-2" adaptor will result in the original clamp tilting the eyepiece and putting the system out of collimation. The only issue you might have is with the resulting focuser being a bit too long or a bit too short. Find the click lock page on Baader's website and there is an image that gives the optical path length for all the different click locks. You can then check at what distance your eyepieces focus (use the scale on the focuser) and, by measuring the height of the 2" clamp and the extension, deduce which combination allows you to focus. With my 8", I removed the extension piece as well as the original clamp. This is a little shorter than the original, and the focuser is racked almost all the way out to focus, plus the only 2" eyepiece I use is lifted out of the clamp by parfocalising rings so that it focuses at the same point as my XWs when they are in the 1.25"-2" clicklock adaptor.

If you do want to change to an alternative 7mm, the Celestron X-Cel LX is a good eyepiece.

As a concept it has been considered before but I doubt there is anyone making such a device commercially. If you do try this I think you want the air blowing across the mirror, not back down onto it. Disrupting the boundary layer of air is the goal rather than cooling the mirror from the front face. I have something similar on my dob, although mine is just a simple flat ring that sits on top of the mirror clips and is more to mask the edge of the mirror rather than redirect air flow from the fan behind. The outer diameter of the first ring I made was matched to the internal diameter of the tube to test if it made any appreciable difference. I could not see any improvement in the image when the fan was turned on, but the passive cooling was severely impeded and the telescope would only cool when the fan was running. As a result I changed to a thinner ring with a gap to allow air to more easily rise up the tube.

This could well be the problem. Looking at the full frame images above, I would say that the telescope is out of collimation. If the collimation is good when viewed through a Cheshire/colimation cap, then a large weight hanging off the focuser could pull the telescope out of collimation when in use, either by focuser sag or via flexing of the OTA tube itself.

Are those photos cropped? Can you post a full frame image?

I have a vague recollection of reading that a secondary mirror that is too small with improperly blackened edges can produce such a spike. If that is true, and the focuser has to be extended further than "normal" then the first thing I would check is that the trusses are properly extended. Secondly I would check that the secondary is properly centred under the focuser as having a bevel on one side of the secondary clipping the light cone instinctively feels more like something that might create an additional pair of spikes. There is also a general mess of mini spikes that I suspect could be cleaned up by masking the primary edge and a weird, wide singular spike that perhaps is just lens flare in the camera used to take the photographs.

The star you check tour collmation on must be exactly in the centre of the FoV. Any off centre star will show a pattern like an uncollimated telescope.

You have chosen the correct focal lengths as suggested by the original post. However, if you are looking at Starguiders instead of Plossls you don't need the barlow to avoid low eye relief. 5/8/12 Starguiders would all work well. You can add the 25mm for your widest field but it will be astigmatic at the edges in an f5 scope. However, I don't know that there is a better alternative at the same price point.

I've not had enough to have personal favourites, but I would go for the Astronomik OIII over the TV Bandmate II OIII. I can't see any obvious difference in the specified spectra and the searchlight data for the 4 filters tested looks more like batch variation rather than a design difference. If you're looking at 2" filters then I think it is better to save yourself the £35 that it costs for the filter to be shipped from Astonomik in Germany, to TeleVue in the USA, and then back to the UK. For the UHC filter, TV have clearly specified a filter without the H-alpha spike. In this case I would happily pay the "TV premium" because it is a different product to the one that Astronomik are selling under their own branding.

Along with the poor image quality that you saw through the 5mm Starguider, which is one of the best two in my opinion, I think this is more likely a sign that the atmospheric conditions were not very good. Try again on another occasion and see if the same issue still occurs. If you have the double star you are trying to split right in the centre of view then you can probably discount any issue with an eyepiece.

That is what the graph suggests, but people using the NBP for example, report seeing some red in or around stars. This suggests to me that those objects must be bright enough to be activating the red cone cells. Likewise, if you see green in a star or nebula, it must be activating the green cones. Once the object becomes so dim that only the rods are activated then it will simply be grey. If this is true then I think I can make some predictions on the use of the DGM NBP vs the TV Bandmate II: The DGM will be better at low magnifications on bright nebulae which have significant red emission. As magnification is increased, and exit pupil reduced, there will come a point where the nebula loses colour, and the TV will become slightly better on those objects as it has a slightly higher transmission in the B-beta/OIII region On dim nebulae, or those lacking a significant red component, the TV will be slightly better for the same reason as in (2). Perhaps @Don Pensack can confirm whether this tallies up with his experiences using both types on different nebulae. Hypothesis 2 is probably the most interesting to me.

You are both right. The response of the eye depends on the lighting conditions. During the day the cones dominate and the response is photopic (black line in the graph below). Here, H-alpha emission is visible. At night the rods dominate and vision becomes scotopic (green line). Under these conditions H-alpha emission is invisible, hence why UHC filters are mainly concerned with the H-beta transmission. Between these two extremes, vision is mespoic and so you might still have some red sensitivity. Also, the following graph shows the scotopic response curve compared to the Hydrogen/OIII emission lines.

Nice find, I think that should be quite a useful tool.

It looks to me like that damage may have occurred in transit. Some of the damage areas look about 120° apart from each other, which suggests that perhaps there was enough space between the mirror and mirror clip supports for the mirror to move. Then, somewhere between the factory and delivery, it has been rattled around hard enough to knock chunks out of the mirror. Also, depending on the manufacturer, they might be quicker at responding than the supplier (although as they have already sent the shipping label, it is probably best to use that route).

Reflection of the secondary spider, I think.

@FLO Given that lots of people are looking at this as a travel scope, do you have a weight for the OTA? What size of mount is likely to be needed? (Assuming the dob base isn't wanted for travel.)

So long as you take care so as not to scratch either mirror, swapping the primary cells and/or mirrors is quite straight forward. If you need to loosen the mirror clips or wash the mirror in future you will be doing the same operation anyway.

So that's why you bought the Hyperion! 🤣 That phone clamp looks quite a good item, it might be a useful accessory for my spotting scope. 🤔

The current one is the best model. Look at the writing on the filter itself in the photo.

It is an original bandmate, not the bandmate type 2 you are looking for.

A 40mm Plossl will have a very restricted AFoV and an exit pupil that is too big. The next option is a 32mm Plossl, which has a nicer AFoV and a 6.4mm exit pupil, which will be fine under dark skies but probably washed out in urban conditions. The option I would look at is a 24mm 68° eyepiece. If you are prepared to play a waiting game, you should be able to find one (or the old version sold under Maxvision/Meade SWA brands) second hand, but you will still need to increase your budget.