I get a lot of Google searches finding my blog with this question and recently I've had a few people email to ask me which I would suggest so I've decided it's time I have somewhere that people can actually find some information on here to help them decide.
Although I'm not going to answer this question for you - just help you decide - I'm not actually sure I could decide between them if I had to pick. Luckily when I decided to get my Holga 135bc (way back in June 2009) that was the only 35mm camera option, the Diana Mini didn't exist, so I didn't need to choose.
The good news is that they are both great little cameras so which ever decision you make, I don't think it will be the wrong one and to be honest, if you love them as much as I do, you'll probably end up getting both anyway...
So, how are these cameras similar?
~ Price ~
When I got my Holga 135bc, it was much cheaper but due to the popularity of Lomography recently, I can safely say that there isn't much difference in the price of these two cameras anymore, even on Ebay. I don't think that's a bad thing though as it makes having to decide on price alone irrelevant.
The Diana Mini can be a bit more expensive if you want the flash included, so if you do want a flash, that is worth considering however I don't think it's completely necessary for either camera to have one as they both work better in natural light anyway.
~ Mechanics ~
Essentially these cameras are very similar - they are both plastic, they can both do multiple exposures, they both have a bulb setting, distance focusing, two aperture settings (sunny or cloudy) and take 35mm film. So if you want to get experimental with your photos, both of these cameras are perfect for that.
What are the differences?
~ Size ~
Though I wouldn't say that this is a deciding factor - it's worth mentioning that the Diana Mini really is indeed mini and that it can be quite fiddly at times whilst the Holga 135 in comparison feels much chunkier and sturdier.
~ Formatting ~
The Diana Mini offers two formats - the half frame and the square format. Whilst the Holga just offers the one, the regular rectangular format to fit the 35mm negative.
This can be a deciding factor between these cameras and I can personally say that one of the reasons that I love my Diana Mini is the square format - it really suits the camera and its results. So if you're looking for the square format in particular then the Diana Mini might be for you.
~ Ease of Use ~
I've written before that it took a lot longer for my Diana Mini to win me over than my Holga 135bc and the Diana Mini is temperamental, it has to be said - I've had issues with loading it, the bulb setting and the advance mechanism, especially in the half frame mode. However, I wouldn't let this put you off - all this requires is practice, patience and research - the Diana Mini micro site has lots of useful videos which I highly recommend looking at and once you've got used to your Diana Mini the results can be constant and glorious.
The Holga 135bc in comparison is much easier to pick up - the loading is quite simple, the buttons aren't as fiddly and the advance mechanism is study. If you're looking for a camera that you can pick up and learn quickly to get the results that you want, then perhaps the Holga 135bc is the camera for you.
~ The Results ~
If you're going to base your decision on anything, then it should really be on this.
Someone once said to me that each camera I use is like a different side of my personality and I think they were right. I use different cameras when I'm in different moods, when I want to share different things and despite being very similar cameras, the results are where these two cameras differ the most.
First we'll look at the Holga 135bc...
The Holga 135bc has an added mask inside the camera that creates the gorgeous vignetting (the 135 doesn't have this but I don't have that camera to compare). The colours and contrasts with the Holga 135bc I've always found to be strong and vibrant, even with softer films like Kodak Portra NC or expired film. The focus is sharper than the Diana Mini with clear lines which create great depth whether the subject is close or further away.
Now the Diana Mini...
In comparison to the Holga 135bc, the Diana Mini results are much softer and dreamier... with subtle contrasts and grain and less vignetting. Yet the Diana Mini is also capable of beautiful colours and focusing, everything just seems more subtle in comparison. With the half frame option you can take double the amount of photos per roll, but I think this camera produces it's best results with the square format.
~ To Summarise ~
The Holga 135bc is a sturdy, reliable camera that is easy to learn and produces images with strong contrasts, gorgeous colours, beautiful vignetting and clear focusing. I always think that this camera captures things almost exactly as I see them.
The Diana Mini is a small, delicate camera which is temperamental, yet with patience and practice can produce dreamy images with soft contrasts, lovely lighting and colours with an almost magical, vintage quality.
It's evident from all the photos above that both of these cameras can produce beautiful photos, especially in bright, natural light. Although the mechanics of the cameras are very similar the lenses in both cameras are different, and it's these differences that will influence your decision on which camera to get and how you take your photos.
~ Other 35mm Cameras to consider ~
Of course, if this is your first 35mm camera then there are other choices to consider as well as these two cameras....
Lomography is very quick to suggest this as a first camera for Lomographers, and it is a great camera - it has extra features to the Diana and Holga including more aperture settings and a light meter which allows for the correct exposure in each photo (though no bulb setting). The contrasts and balance of it's photos are always spot on and the focus is clear - however, this camera is a hefty price. One that I do think is worth it but perhaps not for your first venture into 35mm cameras or if you have a limited budget.
Superheadz Wide and Slim
This camera is simple. It has one shutter button, a fixed wide angle lens and that is it. The colours are vivid with great vignetting and the results can be fun as well are artistic. If you're worried about all the settings on the Diana Mini or Holga 135bc then perhaps this is the camera for you, although you can't do multiple exposures. This camera is cheap and also comes in a fun variety of colours.
Again, similar to the Holga 135bc and Diana Mini in mechanics - it's plastic, it can take multiple exposures, it has a bulb setting, distance focusing, a fixed aperture and takes 35mm film. However, this camera has a wide angle lens which produces great vignetting and interesting results. Another contender if you are looking for something a bit more artistic and varied.
~ See Also ~
This Lomo Flickr thread has a great description and more information on the cameras I've talked about above.